Anna Rita Tufano
email: anna-rita.tufano@ifsttar.fr

Olivier Chiello

Marie-Agnès Pallas

Baldrik Faure

Claire Chaufour

Emanuel Reynaud

Nicolas Vincent

On-board indirect measurements of the acoustic quality of railway track: state-of-the art and simulations

Keywords: Noise mapping, CNOSSOS-EU method, Railway, Rolling Noise, Wheel/Rail Roughness, Track Decay Rate, On-board Measurement I-INCE Classification of Subject

Noise emission is a major concern for residents living along railway lines. For a large range of conventional speeds, railway noise is dominated by rolling noise. The contribution of the track to rolling noise is mainly driven by the level of rail roughness and the Track Decay Rate (TDR). The MEEQUAI project (on-board measurement of the acoustic quality of the infrastructure) aims to develop a system capable of measuring these characteristics using on-board instrumentation. A state-of-the-art on the subject shows that indirect measurement from vibro-acoustic sensors like axle-box accelerometers or microphones in the bogie area seems possible, but that a number of improvements could be made to the existing methods, especially in estimating the transfer functions between the effective roughness and the signals provided by the sensors. The idea is to combine modelling and measurements to optimize the estimation of the transfer functions and the location of sensors while taking into account the variability of circulated tracks. Numerical analyses of transfer functions based on axle/track vibro-acoustic models are performed. Based on the simulations results, several improvements are proposed, with a view to future tests in rolling conditions.

INTRODUCTION

Environmental railway noise is a critical issue, both for welfare and legal practices. In order to guarantee a good acoustic environment, national and international laws are regularly established; among these, the European directive 2002/49/CE relates to the assessment and management of environmental noise. This directive requires Member States to realise "noise maps" and to set up action plans, in case noise issues exist.

A common methodology for the calculation of railway noise is prescribed to Member States: CNOSSOS-EU (Common NOise aSSessment methOds). One of the main features of this methodology, is that it requires input data that are typical of each noise source, instead of generic source power terms. This approach allows establishing action plans that are optimized both from the viewpoint of noise reduction and cost. Accordingly, railway rolling noise should be described through a set of track and train physical and mechanical parameters; rail roughness and Track Decay Rate (TDR) are the most influential parameters concerning the track contribution. Thus, the relevance of CNOSSOS noise maps, is linked to the quality of these input data. The measurement of rail roughness and TDR is nowadays performed on small track portions, with a high cost (need to stop the train circulation on the track portion, and slow measurement protocols).

The MEEQUAI project (on-board measurement of the acoustic quality of the infrastructure) aims at developing an industrial prototype for the on-board measurement of roughness and TDR. The MEEQUAI system lies on an inverse problem on rolling noise: the aim is to estimate the track acoustic characteristics from vibro-acoustic sensors placed on the train.

In addition to the collection of input data for noise maps, the MEEQUAI measurement system should provide brand-new solutions for maintenance and monitoring. The main asset of an on-board system is the opportunity to perform measurements on long track portions. This would allow to better identify the influence of track parameters on the acoustic quality of railways, and to efficiently manage noise action plans. Moreover, the sensors would simultaneously collect signals related to the state of track, thus giving information on rail defects, joints and switch. The monitoring of these hotspots is time-consuming and expensive with current procedures.

Railway noise is related to several sources, such as rolling noise (caused by the railwheel contact), traction noise from equipment, aerodynamic noise. The contribution of each of these sources depends on train speed, but for a large range of operational speeds, rolling noise can be considered as the main source [START_REF] Thompson | Railway Noise and Vibration: Mechanisms, Modelling and Means of Control[END_REF].

Roughness on the wheel and rail running surfaces induces vertical vibration of the wheel and rail systems, that are influenced by physical phenomena acting at the railwheel contact. The main wavelengths of roughness that are relevant to acoustic issues, are between about 5 and 500 mm. The vibration is transmitted into the wheel and track structures, leading to sound radiation.

TRACK CHARACTERISTICS MEASUREMENT

Two kinds of methodologies exist for assessing roughness and TDR: direct or indirect measurements.

Direct roughness measurement consists in estimating the vertical irregularities of the two rails using fixed measuring rules or mobile trolleys. Direct measurement of the TDR consists in estimating the attenuation of vertical and lateral vibration waves along the rail using a fixed accelerometer and mobile impact hammer excitation.

Unlike direct measurements where sensors are applied directly to the rail surface, indirect measurements focus on quantities that result from wheel/rail interaction, such as noise or vibrations of axle-boxes or rail, and from which the actual combined roughness and/or TDRs are deduced. Indirect measurements are made in the time domain. They can be performed in a fixed frame (pass-by measurement) or on the train itself (on-board measurement).

Direct measurements have a number of advantages over indirect measurements: they allow the separation of rail and wheel contributions, they are accurate and free from perturbations coming from the railway environment. That is why they are the only measurement methodologies accepted in a normative framework (standards EN 15461 and EN 15610). Nevertheless, direct measurements require stopping train traffic, and are thus limited to small track portions.

Roughness measurement through axle box accelerometers

Roughness can be estimated from axle-box acceleration Γ B.E. ( f ). For a single rail, one can estimate effective roughness as:

|r e f f | 2 = |H r-B.E. | 2 |Γ B.E. | 2 (1)
where |H r-B.E. | is the roughness-axle box acceleration transfer function. This method, originally proposed by British Rail Research [START_REF] Lewis | A new method for the routine measurement of rail head corrugations[END_REF] is exploited by the Swedish railway company Banverket (TRC "Strix" [START_REF] Spannar | A new approach of assessing rail roughness[END_REF]), and for the RailMeasurement "High Speed Rail Corrugation Analyser" (HSRCA) [START_REF] Bongini | Noise mapping "of a railway network: Validation and use of a system based on measurement of axlebox vibration[END_REF]. The correctness of the method has been proved in the framework of the TRANRED project, on the London subway [START_REF] Vincent | Technical support for the TRANRED project[END_REF]. A similar technique has been proposed for the rail surface monitoring, during the MONA project [START_REF] Vincent | Aide à la conception d'un cahier des charges pour une chaîne de mesure acoustique du bruit de roulement[END_REF]. Some information is available on the setup and validation of this methodology on the Czech railway network by VUKV [START_REF] Phamová | Indirect method of rail roughness measurement -VUKV implementation and initial results[END_REF].

Roughness measurement through microphones

Early systems exploiting microphone signals were based on a comparison of measured noise levels with noise patterns; these systems do not allow to estimate an absolute roughness spectrum. This methodology has been employed in the ABN system (AxleBox Noise measuring device) [START_REF] Bracciali | Continuous external train noise measurements through an On-Board device[END_REF], the system proposed in the framework of the MONA project [START_REF] Vincent | Aide à la conception d'un cahier des charges pour une chaîne de mesure acoustique du bruit de roulement[END_REF], the NoiseMon system developed for the British railway network [START_REF] Hardy | The influence of real-world rail head roughness on railway noise prediction[END_REF], and the SMT (Specially Monitored Track) system developed by the Deutsche Bahn [START_REF] Asmussen | Status and perspectives of the "Specially Monitored Track[END_REF].

More recently, it has been proposed to use transfer functions, to estimate effective roughness spectra r e f f ( f ) from pressure p( f ) measured by on-board microphones:

|r e f f | 2 = |H r-p | 2 |p| 2 (2)
where |H r-p | is the roughness-acoustic pressure transfer function. Different measurement systems are available, each with a specific technique for estimating the transfer function (experimentally or numerically) and a determined number and position of microphones. Among these, the ARRoW (Acoustic Rail-Influence Recording on Wheels) system [START_REF] Kuijpers | Indirect rail roughness measurement: The ARRoW system within the LECAV project[END_REF], the SNCF LECAV method which has not been tested on a rolling train yet [START_REF] Chartrain | Lecture acoustique de la voie ferrée[END_REF], the system developed in the framework of the Quiet Track project and tested on the Stockholm subway [START_REF] Höjer | Monitoring system for track roughness[END_REF], the Belgian Infrabel system, and the Danish SWECO system.

Other roughness measurement techniques

Other systems exist for roughness measurement, which are based on optical techniques [START_REF] Fidecaro | Interferometric rail roughness measurement at train operational speed[END_REF], eddy current sensors, or strain gauges fixed on wheels. However, these systems are hardly fitted on vehicles in operational conditions.

MEEQUAI strategy

The systems and methodologies presented in previous sections are summarized in Table 1. These methods suffer from certain limitations. First, their relevant frequency range is limited. An optimisation of the position of sensors allows overcoming this limitation; moreover, the combination of different types of sensors (as proposed in the LECAV method [START_REF] Chartrain | Lecture acoustique de la voie ferrée[END_REF]) is convenient in terms of frequency range of application.

Frequency range

The second limitation is linked to the precision of transfer functions, which are usually measured during calibration tests. The calibration neither take into account the variability of parameters that can influence track dynamics (such as sleeper and railpad configuration), nor the variability of kinematic parameters (train speed and contact point position); all these parameters directly affect the shape of transfer functions. Combining numerical and experimental methods for the estimation of transfer functions is a way to overcome this weakness.

Further constraints can be related to acoustic or vibration perturbations, as well as couplings between the two rail sides. Sensor redundancy in the context of inverse methods techniques can improve the quality of the acquired signal, and is a solution to deal with this constraints.

Finally, there are few cases of measurement systems of the track dynamic characteristics: on the LECAV method [START_REF] Chartrain | Lecture acoustique de la voie ferrée[END_REF], pairs of microphones measure the acoustic signal in the rail near-field, and compare it to a benchmark of related track architectures; in the framework of the Quiet Track project, the difference between noise levels measured in the wheel vicinity and under the coach, allows calculating the TDR [START_REF] Höjer | QUIET-TRACK -WP 1. Monitoring system for noise related track parameters and severe wear[END_REF]. The first system has not been tested in operational conditions, while the latter gives inaccurate results. A method based on rail near-field microphones seems to be the most effective to be investigated: it does not depend on the level of excitation (since relative signals are considered), and the comparison with benchmark signals (eventually obtained by numerical simulation) makes it a robust procedure.

The idea behind the MEEQUAI system is to set up a measurement system for roughness and for the track dynamics characteristics, that overcome the mentioned limitations, and is based on the solutions proposed for each one of those limitations.

NUMERICAL ANALYSES

Numerical analyses have been performed, in order to estimate numerically the transfer functions needed for the methods introduced in Section 2. Moreover, numerical simulations helps optimising the number and position of on-board sensors, and to analyse the reliability and variability of sensor signals.

Rail-wheel interaction and track variability

In order to calculate the acceleration-roughness transfer function, one first needs to estimate the relationship between roughness and dynamic forces at contact. This relationship can be easily inferred from a wheel-rail interaction scheme, like the one proposed in [START_REF] Thompson | Railway Noise and Vibration: Mechanisms, Modelling and Means of Control[END_REF] and recalled in Figure 1. Displacements of the wheel, rail, and contact subsystems x W , x R , x C , are related to the dynamic force at contact F by the relations:

x W = A W F W x R = A R F R x C = A C F C (3)
where A W , A R and A C are the receptance matrices at contact point, for the wheel, rail, and contact subsystem respectively. By continuity of displacements at the contact point, displacements can be related to the effective roughness r e f f :

r e f f = x R + x W -x C (4)
Therefore, by imposing the equilibrium of forces at contact:

F = A -1 r e f f = A R + A W + A C -1 r e f f (5)
Receptance matrices can comprise coupling terms between different directions, and between the two rail sides. In this paper, we only consider the lateral and vertical directions of the track reference system, thus dealing with a 4x4 size matrix problem. Terms of matrices A W and A R are obtained by Finite Element calculation on track and wheelset models (see Figure 2 for these FE models); terms of matrix A C are obtained analytically, based on the Hertz contact theory, where additional lateral creep terms have been taken into account [START_REF] Thompson | Railway Noise and Vibration: Mechanisms, Modelling and Means of Control[END_REF].

The track F.E. model is composed of solid elements for rail and sleeper, while railpads and ballast are modelled as discrete springs. In order to simulate an infinite rail length, "anechoic terminations" are included: rail material damping is gradually increased when moving towards the rail end, thus preventing any reflections at the end. This modelling strategy is compliant for the calculation of TDR.

Several track configurations have been modelled by Finite Elements, so that the variability of transfer functions with track parameters could be analysed. The parameters which are considered are: track platform (ballast / concrete platform), railpad dynamic properties (stiffness and damping), rail profile, sleeper configuration (mono/bi-bloc concrete, wood). Thanks to this sensitivity analysis, we have determined the most influential parameters for the track dynamic behaviour: railpad stiffness, sleeper mass, and track platform.

The weelset F.E. model is composed of solid elements for all the components (wheel, axle, brakes, axlebox), except for bearings, which are simulated through a set of discrete springs in a radial pattern.

Axle box acceleration -roughness transfer functions

Axle box acceleration can be calculated from mechanical transfer functions between the contact point and a point on the axle box:

Γ B.E. = B W F = B W A -1 r e f f (6)
Inertance matrix B W terms are derived from the same F.E. calculations that give the receptance matrix elements. The equations presented here are the core of a Matlab R code that allows evaluating the rail-wheel contact (Figure 3).

The wheelset selected to test the method belongs to a SNCF Corail train. An Experimental Modal Analysis test campaign has been realized on this wheelset, in order to validate the FE model in the frequency range [50-2000 Hz]. The validation of the axle box components happens to be challenging, when bearing data are not completely. That is why, it has been decided to use measured B W terms and to rely on numerical data only when a fully validated FE model is available; numerical A W terms are more easily correlated, and can be used even when wheelset data lacks. Therefore, what is foreseen is an hybrid numerical/experimental calibration methodology, depending on the availability of wheelset data.

Acoustic pressure -roughness transfer functions

Acoustic wheel and track near-fields have been calculated by solving an exterior radiation problem on an acoustic Finite Element model. For both structures, a weak fluid-structure coupling has been assumed. The acoustic boundary condition is enforced as a displacement field on the structure surface, which has been calculated through F.E. calculations on the models of Figure 2, for a unit vertical force at the wheel-rail contact. The acoustic mesh is fitted to the frequency range: different meshes are used for single frequency ranges, and each mesh is designed to have 4 elements per wavelength. Far-field conditions are simulated through Infinite Elements, whose interpolation order is carefully chosen to attain convergence on power indexes. A baffle plane is included, in order to take into account the ballast. In addition, ballast acoustic absorption properties are included in the model, through an impedance boundary condition on the baffle plane; the impedance values are determined analytically and based on a Delany-Bazley model [START_REF] Thompson | Railway Noise and Vibration: Mechanisms, Modelling and Means of Control[END_REF].

For wheel radiation, the attention has been focused on wheel resonances up to 5 kHz, and in particular on Rn (radial modes with n nodal diameters) and 1Ln modes (axial modes with 1 nodal circle and n nodal diameters), which contribute the most to rolling noise. The acoustic pressure field has therefore been estimated at wheel resonances; as an example, Figure 4 shows the pressure field at the frequency corresponding to the wheel R2 mode (larger contribution to rolling noise). The general trend for the pressure field, as frequency increases, is to become more and more complex and directional, as a result of acoustic waves recombinations. As a whole, the field pressure is more homogeneous at frequency corresponding to wheel radial modes, than at axial modes. The presence of a partially absorbing baffle makes the acoustic field way more complex than the case of a free wheel in space.

It is possible to identify an optimal position for the microphone, based on two requirements on the acoustic near-field impedance, Z = p ρ 0 c 0 V n :

-Z should be stable along a line that runs out of the wheel, so that some flexibility on the exact microphone position can be allowed;

-|Z | should be as close as possible to unity, in order to limit errors in the transfer function calibration. Concerning track radiation, the analysis has been focused on 20 frequencies in the [0 -2000 Hz] range. The track model includes 8 sleepers; this track length has been chosen as a good comprise between a reliable representation of the track dynamics in the longitudinal direction, and computational burden (which can be quite high for truck structures). As an example, Figure 5 shows the acoustic pressure field around the track, at 1 KHz. The rail on which the vertical force is applied, is the one the negative y side; this is also visible in the acoustic field, since this rail radiates the most. The pressure field is quite stationary in the longitudinal direction, and radiation patterns are clearly visible in this direction: this is though to be due to the proximity of the so called "pinned-pinned frequency". Based on the criterion already introduced for the wheel radiation, an optimized position for the rail near-field microphone has been identified. The detailed position of the wheel and rail near-field microphones is outside the scope of this paper.

Future static tests will validate the numerical analyses, and confirm the positions hence identified. The definite sensor positions will allow defining the design of the MEEQUAI prototype; a final test campaign will consist in measurements of transfer functions in operational conditions.

CONCLUSIONS

On-board measurement of the track acoustic quality is necessary to characterize the railway network on a wide scale. The challenge not only concerns the input data for noise maps, but is also critical with respect to maintenance action plans. A state-of-the-art shows that indirect measurements of roughness and track dynamic characteristics from on-board vibro-acoustic sensors is viable, but a number of improvements is necessary, especially when concerning to the estimation of transfer functions. The MEEQUAI project aims at combining calculation and measurement, optimizing the estimation of transfer functions and the position of sensors, and taking into account the variability of track architectures. Finite Element simulations have been performed, to calculate the axle box-roughness and acoustic pressure-roughness transfer functions. Upcoming actions of the project involve the validation of calculation through static tests, and the development and test of inverse methods in operational conditions.

Figure 1 :

 1 Figure 1: Wheel-rail interaction scheme.

Figure 2 :

 2 Figure 2: Finite Element models for track and wheelset.

Figure 3 :

 3 Figure 3: Code schematics for the wheel-rail interaction.

Figure 4 :

 4 Figure 4: Wheel acoustic near-field [in dB] at 1646 Hz (R2)

Figure 5 :

 5 Figure 5: Track acoustic near-field [in dB] at 1 kHz.

Table 1 :

 1 Review of on-board roughness measurement systems.

		Sensors	Measurement system
	100-600 / 1000 Hz	Axle box accelerometers	TRC Strix, HSRCA, TRANRED
	500 / 1000 -1500 Hz Rail near-field microphone	LECAV
	500 / 1000 -5000 Hz Under coach microphone	MONA, Quiet Track
	1500 -5000 Hz	Wheel near-field microphone ARRoW, LECAV, SWECO

ACKNOWLEDGEMENTS

The MEEQUAI project has been selected in the framework of the call for projects FUI-AAP23 of the Inter-minister Unique Fund (FUI). It is funded by the Public Bank of Investment (BPI France) and by the AURA Region via the European Funds for Regional Developments (FEDER). This project is co-financed by the European Union.

This work was supported by the LabEx CeLyA of Université of Lyon, operated by the French National Research Agency (ANR-10-LABX-0060/ANR-11-IDEX-0007). This support is greatly appreciated.


Thi Huyen Vu

Nguyet-Thanh Ha-Duong

Alexandra Aubry

Estelle Capton

Pierre Fechter

Patrick Plésiat

Philippe Verbeke

In vitro Activities of a New Fluoroquinolone Derivative Highly Active against Chlamydia trachomatis

Keywords: Inhibitors, 8-hydroxyquinoline, ciprofloxacin, Gram-negative, Gram-positive

Chlamydia trachomatis is a bacterial human pathogen responsible for the development of trachoma, an infection leading to blindness, and is also the cause of the main bacterial sexually transmitted infection worldwide. We designed a new inhibitor of this bacterium with, however, some prerequisites using (i) the iron dependency of the bacterium, (ii) a commercially available broad-spectrum antibiotic and (iii) a short synthetic pathway. The corresponding 8hydroxyquinoline-ciprofloxacin conjugate was evaluated against a panel of pathogenic bacteria, including C. trachomatis but also the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter

species). Its anti-Chlamydia activity is higher than that of ciprofloxacin and seems to be related to the fluoroquinolone moiety of the molecule, which is also responsible for the complexation of iron(III), as demonstrated by spectrophotometric titration.

Chlamydia trachomatis (C. trachomatis), an obligate intracellular Gram-negative bacterium, is responsible for the most common sexually transmitted bacterial infection in the world (131 million new cases in 2012, WHO data), [START_REF] Verbeke | WHO guidelines for the treatment of Chlamydia trachomatis[END_REF] which causes severe complications leading to serious sequelae in men and women, including infertility. This infection also facilitates other sexually transmitted infections (STI), including HIV, [START_REF] Venkatesh | The relative contribution of viral and bacterial sexually transmitted infections on HIV acquisition in southern African women in the Methods for Improving Reproductive Health in Africa study[END_REF][START_REF] Peterman | Risk for HIV following a diagnosis of syphilis, gonorrhoea or chlamydia: 328,456 women in Florida, 2000-2011[END_REF] and increases the incidence and persistence of human papillomavirus (HPV) infection. [START_REF] Seraceni | High prevalence of hpv multiple genotypes in women with persistent Chlamydia trachomatis infection[END_REF][START_REF] Vriend | Medical Microbiological Laboratories and the CSI group. Incidence and persistence of carcinogenic genital human papillomavirus infections in young women with or without Chlamydia trachomatis co-infection[END_REF] C. trachomatis is also responsible for trachoma, the most common infectious cause of blindness. [START_REF] Mariotti | Trachoma: global magnitude of a preventable cause of blindness[END_REF] Treatment of C. trachomatis infection requires special considerations related to the bacterial cycle. Indeed, infectious elementary bodies are metabolically inert and insensitive to antibiotics which target bacterial replication (fluoroquinolones) and translation (macrolides, tetracyclines). Effective antibiotics must target the metabolically active reticulate bodies, which replicate in an intracellular inclusion. Lipophilic antibiotics such as azithromycin (octanol-water partition coefficient, log P = 4.02) [START_REF] Mcfarland | Quantitative structure-activity relationships among macrolide antibacterial agents: in vitro and in vivo potency against Pasteurella multocida[END_REF] reach very high intracellular concentrations, which explains their good bactericidal activity against Gram-negative bacteria such as C. trachomatis. [START_REF] Mcorist | Obligate intracellular bacteria and antibiotic resistance[END_REF][START_REF] Samra | In vitro susceptibility of recent clinical isolates of Chlamydia trachomatis to macrolides and tetracyclines[END_REF] Drug-resistant C. trachomatis has rarely been reported. [START_REF] Sandoz | Antibiotic resistance in Chlamydiae[END_REF] However, under the unfavorable conditions produced, for example, by treatment, bacteria can enter into a persistent form, which is viable, nonreplicative and less sensitive to antibiotics; it has not yet been isolated in vivo. [START_REF] Hogan | Chlamydial persistence: beyond the biphasic paradigm[END_REF] This persistent form can remain for several months/years in infected tissues, causing recurrent infections, chronic inflammation and tissue fibrosis. Consequently, treatment failure, which is observed in 5-23% of cases, could be the result of the re-emergence of the persistent infection. [START_REF] Horner | Azithromycin antimicrobial resistance and genital. Chlamydia trachomatis infection: duration of therapy may be the key to improving efficacy[END_REF] Moreover, the persistent form of C. pneumoniae (responsible for respiratory infections) is suspected to spread to other tissues and to be responsible for arthritis, atherosclerosis, endocarditis and asthma. [START_REF] Hahn | Chlamydia pneumoniae as a respiratory pathogen[END_REF] Thus, incomplete antibiotic efficacy may be due to a lack of sensitivity of persistent forms of Chlamydiaceae but also to modest intracellular concentrations of the conventionally prescribed drugs. All these elements highlight the importance of seeking new antibiotics against Chlamydiaceae.

C. trachomatis needs iron to grow. Salicylidene acylhydrazides (Figure 1), inhibitors of the Chlamydial type III secretion system (T3SS) with iron-chelating properties, inhibit C. trachomatis growth through a mechanism partially involving iron restriction, with minimal bactericidal concentrations (MBC) lower than 50 µM. [START_REF] Slepenkin | Reversal of the antichlamydial activity of putative type III secretion inhibitors by iron[END_REF] The absence of cytotoxicity to HeLa 229 cells enables their use as vaginal microbiocides. [START_REF] Chu | Candidate vaginal microbicides with activity against Chlamydia trachomatis and Neisseria gonorrhoeae[END_REF][START_REF] Ur-Rehman | Pre-clinical pharmacokinetics and anti-chlamydial activity of salicylidene acylhydrazide inhibitors of bacterial type III secretion[END_REF] We previously synthesized 3-isoxazolidinone derivatives, with iron-chelating properties, as equally effective inhibitors of bacterial growth (compounds 17-19; 25 < MBC < 50 µM; Figure 1), without toxicity at 200 µM. However, since the antibacterial activity of 19 is not reversed by excess iron(III), metal chelation cannot be the only mechanism of action of these compounds. 17 [START_REF] Abdelsayed | Design and synthesis of 3-isoxazolidone derivatives as new Chlamydia trachomatis inhibitors[END_REF] In the present work, we synthesize a new inhibitor of this bacterium with, however, some prerequisites, using: (i) the iron dependency of the bacterium, (ii) a commercially available broadspectrum antibiotic and (iii) a short synthetic pathway. We opted for a fluoroquinolone, ciprofloxacin, with the objective of obtaining more active derivatives than the parent antibiotic and, therefore, potentially useful for the treatment of C. trachomatis infection. We have selected conventionally described metal-chelating entities such as catechol, which forms extremely stable complexes with iron(III). [START_REF] Karpishin | Spectroscopic studies of the electronic structure of iron(III) tris(catecholates)[END_REF] This very high stability explains why the catechol group is present in many siderophores, molecules which are synthesized by microorganisms to trap iron in the external environment in order to facilitate its intracellular transport. trachomatis serovar L2 strain as previously described. [START_REF] Dumoux | Penicillin kills Chlamydia following the fusion of bacteria with lysosomes and prevents genital inflammatory lesions in C. muridarum-infected mice[END_REF] Infection was performed with or without the test molecules (0-50 µM) and with or without iron citrate (200 µM). 72 h post-infection, cell lysates were processed and used to infect new HeLa cells. The reinfection capacity was scored by calculating the Inclusion Forming Unit (IFU) of each cellular lysate. Ciprofloxacin (black bars) was used as external control. The results presented in Figure 3 show that the Minimal Bactericidal Concentration of ciprofloxacin (MBC > 16.5 µg/mL or > 50 µM) is similar to that described in the literature (> 10 µg/mL) [START_REF] Rumpianesi | In vitro activity of ciprofloxacin against Chlamydia trachomatis and Ureaplasma urealyticum[END_REF] while compound 1 (grey bars) presents a MBC of 2-5 µg/mL (5-10 µM). Therefore, functionalization of the fluoroquinolone nitrogen by an 8-hydroxyquinoline entity does not inhibit its antibacterial activity. The resulting compound is even more active than the parent molecule, probably due to a gain in lipophilicity. Indeed, its calculated octanol-water partition coefficient (cLog) is higher than that of ciprofloxacin (cLogP(ciprofloxacin) = 1.32 vs cLog P(1) = 3.09). 23 Under the same conditions, the catechol analogue 2 is inactive (data not shown).

Iron is an essential element for C. trachomatis. However, to date, no siderophores or siderophore receptors have been described in Chlamydiaceae. [START_REF] Stephens | Genomic autobiographies of Chlamydiae[END_REF] Since catechol is one of the most powerful ironchelating agents, the inactivity of compound 2 against C. trachomatis suggests that the inhibition induced by compound 1 is not mainly due to iron chelation.

Taking into account the iron-chelating properties of both entities, 8-hydroxyquinoline and the fluoroquinolone, we evaluated the ability of iron(III) to reverse the inhibitory effect of compound 1 by adding exogenous iron citrate (200 µM). The results presented in Figure 4 show that the inhibitory effect of compound 1 is only partially reversed by excess Fe 3+ (20%, 35% and 60% decrease at 1, 2.5 and 5 µM, respectively), confirming that iron chelation is not its main antibacterial mechanism. To further characterize compound 1, its ability to complex Fe 3+ was studied by spectrophotometric titration. Complexation was performed in a H 2 O/DMSO (1:1; v/v) mixture to avoid precipitation of any ligand and/or complex. The pH values mentioned are those of aqueous solutions before mixing with DMSO. Compound 1 has two potential sites for metal complexation: the ciprofloxacin carboxylate and keto groups and the 8-hydroxyquinoline part. At pH 2, the addition of FeCl 3 to a solution of 1 leads to a bathochromic shift (red shift) of the - band from 284 to 290 nm and the appearance of a ligandto-metal charge-transfer (LMCT) band at 450 nm (Figure 5). The latter is identical to the LMCT of a complex between iron(III) and ciprofloxacin described by Fardeau et al., [START_REF] Fardeau | Synthesis and antibacterial activity of catecholate-ciprofloxacin conjugates[END_REF] whereas those of the complex between Fe 3+ and 8-hydroxyquinoline are observed at 481 and 632 nm (not shown). This result suggests that only the fluoroquinolone part of compound 1 complexes Fe 3+ at this pH.

Furthermore, at pH 7.4, iron-exchange experiments between Fe-nitrilotriacetic acid (Fe-NTA), a chelating agent, and 1 or methyl 8-hydroxyquinoline-2-carboxylate, a surrogate of the 8hydroxyquinoline moiety, show also differences in the LMCT bands (see Figure S1, Supplementary Information).

An isosbestic point at 340 nm indicates the formation of a single iron complex. The inset in Figure 5 presents the plot of the absorbance at 450 nm against the ratio [Fe(III)]/ [1]: an increase in the absorbance is followed by a plateau. The two asymptotes intersect at a ratio of 1, implying a 1:1 stoichiometry (metal-ligand) for the complex. We then determined the affinity constant of the complex at pH 2, using Specfit analysis of the spectra; this is low (K 11 = 2.5 ± 0.3), which confirms that iron chelation is not the main antibacterial mechanism of action of this compound. trachomatis infection with one of the following drugs: azithromycin (1 g orally as a single dose) or doxycycline (100 mg twice a day for 7 days). The in cellulo anti-chlamydia bactericidal activities of both compounds have been published: doxycycline and azithromycin have MBCs of 2.5-5.0 µg/mL and 10-50 µg/mL, respectively. [START_REF] Reveneau | Bactericidal activity of first-choice antibiotics against gamma interferon-induced persistent infection of human epithelial cells by Chlamydia trachomatis[END_REF] Compound 1 is therefore at least as effective in cellulo as these two molecules.

Ciprofloxacin is a broad-spectrum antibiotic. We therefore looked at the ability of compound 1 to inhibit other human pathogens, including Gram-negative and Gram-positive bacteria from the ESKAPE group, an acronym including pathogenic bacteria present in the hospital environment and difficult to treat (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species). Staphylococcus aureus is the most common staphylococcus strain responsible for human diseases, particularly nosocomial infections, along with Escherichia coli. The minimal inhibitory concentrations (MIC) of the derivatives were then determined (Supplementary Information) (Table 1). Many microbes, including P. aeruginosa strains, are well known to synthesize siderophores to scavenge iron from their environment. In order to facilitate the transport of antibiotics into bacteria, siderophore-conjugates have been described and used in a Trojan-horse strategy. [START_REF] Cézard | Chemistry and biology of pyoverdines, Pseudomonas primary siderophores[END_REF] Compound 2 was previously described as a new antibiotic following this strategy. [START_REF] Fardeau | Synthesis and antibacterial activity of catecholate-ciprofloxacin conjugates[END_REF] Indeed, in iron-deficient culture conditions only, compound 2 is active against the P.

aeruginosa DSM 1117 susceptible strain with a MIC of 32 µg/mL, suggesting effective transport of the corresponding iron(III) complex by bacterial iron-uptake pathways. We found that compound 2 is inactive against P. aeruginosa ATCC-27853, a reference strain (MIC > 128 µg/mL, Table 1), unlike compound 1 (MIC = 4 µg/mL).

While inactive against M. tuberculosis, compound 1 exhibits inhibitory activity against all the other Gram-negative and Gram-positive bacteria tested. For instance, it stops the growth of E. coli (MIC ≤ 0.06 μg/mL), probably by inhibition of its DNA gyrase, one of the bacterial targets of quinolones (IC 50 = 8-16 μg/mL; Table 1 and Supplementary Information). In fact, this compound has a panel of interesting antibacterial activities, in that the MICs obtained are in the μg/mL range. However, this molecule is systematically less active than the parent antibiotic, ciprofloxacin, except for S. aureus, especially against laboratory and clinical isolates.

As already observed for C. trachomatis, the catechol analogue 2 is less potent than the 8hydroxyquinoline derivative 1 on the panel of bacteria tested.

The starting acid 3 was tested in order to evaluate its contribution to the antibacterial activity of compound 1. The results (Table 1) show that whatever the pathogen, this acid is inactive, which suggests that the fluoroquinolone part of 1 is responsible for its efficacy. We report here the synthesis of a novel ciprofloxacin derivative by a single-step coupling of the parent antibiotic. This compound has notable antibacterial activity against Gram-negative and Grampositive bacteria, including the obligate intracellular bacterium C. trachomatis. However, only its antichlamydial activity is higher than that of the parent antibiotic. This antibacterial effect is only partially reversed by the addition of iron(III), which is complexed by the fluoroquinolone part of the molecule.

Fig. 1 .

 1 Fig.1. Previously described inhibitors of C. trachomatis.[START_REF] Abdelsayed | Design and synthesis of 3-isoxazolidone derivatives as new Chlamydia trachomatis inhibitors[END_REF]

The 8 -

 8 hydroxyquinoline entity, present in O-Trensox, a potent synthetic iron chelator,[START_REF] Baret | O-TRENSOX: A Promising water-soluble iron chelator (Both FeIII and FeII) potentially suitable for plant nutrition and iron chelation therapy[END_REF] also attracted our attention. Both cathechol and 8-hydroxyquinoline were used via the corresponding carboxylic acids (Figure2).

Fig. 2 .

 2 Fig. 2. Starting materials.

Fig. 3 .

 3 Fig. 3. Inhibitory effects on C. trachomatis infectious capacity of compounds tested in cellulo (grey bars: compound 1; black bars: ciprofloxacin. Statistically significant differences are noted as follows: ** p<0.01, *** p<0.001).

Fig. 4 .

 4 Fig. 4. Compound 1 inhibitory effect in the presence of excess iron citrate (200 µM). Statistically significant differences are noted as follows: * p<0.05, ** p<0.01, *** p<0.001.

Fig. 5 .

 5 Fig. 5. Absorption spectra of 1 (10 -4 M) in presence of increasing concentrations of FeCl 3 (0-10 -3 M) at pH 2 and 25±0.5 °C. Absorbance at 450 nm plotted against [Fe(III)]/[1] in inset.

Table 1 .

 1 In vitro antibacterial activities (IC 50 or MIC) of compounds 1-2, ciprofloxacin and acid 3:

	Organism		Gram a	Ciprofloxacin	1	2	3
	M. tuberculosis		-	12-17 b,c	>128 b	>128 b	>128 b
	E. coli		N	1-2.9 b	816 b	415 b	>128 b
	E. coli ATCC-25922	N	≤ 0.06 d	≤0.06 d	nd	>8 d
	K. pneumoniae ATCC-700603	N	0.25 d	4 d	nd	>8 d
	P. aeruginosa ATCC-27853 e	N	0.25 d	4 d	>128 f	>8 d
	A. baumannii CIP-7010	N	0.125 d	2 d	nd	>8 d
	S. aureus HG001 (laboratory strain)	P	0.125 d	0.0625 d	5 d	nd
	S. aureus ATCC-25923 (clinical	P	0.25 d	0.125 d	nd	>8 d
	isolate)
	S. aureus ATCC-700699 (resistant	P	>8 d	>8 d	nd	>8 d
	isolate)
	S. epidermis ATCC-14990	P	0.125 d	0.25 d	nd	>8 d
	ATCC-35984	P	≤0.06 c	≤0.06 d		>8 d
	E. faecalis	JH2-2	P	2 d	8 c	nd	>8 d
		UCN41	P	1 d	8 d	nd	>8 d
	E. faecium ATCC-19434T	P	1 d	8 d	nd	>8 d
	BM-4147	P	4 d	>8 d	nd	>8 d

a P/N : positive/negative. b IC 50 (µg/mL) against wild-type DNA gyrases of M. tuberculosis and E. coli. c IC 50 s slightly higher than those previously determined. 27 d MIC (µg/mL).

e Similar MIC were obtained against P. aeruginosa PAO1, a laboratory strain (data not shown). f P. aeruginosa DSM 1117.

20 nd: not determined.

Acknowledgments

This work was supported by a Ph.D. grant from the University of Science and Technology of Hanoi (Vu T.H.). The Institut des Humanités de Paris (Paris Diderot), the National Center for Scientific Research

(CNRS) and the University Paris Diderot are gratefully thanked for financial support. Sébastien Bellynck is also sincerely thanked for his technical assistance. We thank Dr. John S. Lomas for carefully reading the manuscript.

Supplementary data

Supplementary data associated with this article can be found in the online version.


Jean-François Lalande

Pierre Graux

Tomás Concepción

Orchestrating Android Malware Experiments

Experimenting with Android malware requires to manipulate a large amount of samples and to chain multiple analyses. Scripting such a sequence of analyses on a large malware dataset becomes a challenge: the analysis has to handle fails on the computer and crashes on the used smartphone, in case of dynamic analyses. We present a new tool, PyMaO, for handling such experiments on a regular desktop PC with the highest performance throughput. PyMaO helps to write sequences of analyses and handle partial experiments that should be restarted after a crash or continued with new unknown analyses. The tool also offers a post processing capability for generating number tables or bar graphs from the analyzed datasets.

I. INTRODUCTION

Researchers working on malware analysis usually performs benchmarks on large datasets of malware samples [START_REF] Lindorfer | ANDRUBIS -1,000,000 Apps Later: A View on Current Android Malware Behaviors[END_REF], [START_REF] Bierma | Andlantis: Large-scale android dynamic analysis[END_REF]. These datasets can contain malicious applications, benign applications or both, and eventually some metadata that help to investigate the samples. When experimenting with these datasets, the samples are consumed by the software that perform a bunch of analysis. Analysis can be either static or dynamic. For example, a static analysis can open the APK file of the sample and perform an analysis of the resources and of the application bytecode. On the other hand, a dynamic analysis may execute the application in an emulator or real smartphone for extracting dynamic events. The obtained artifacts are then collected and can feed another step of the experiment, for example a machine learning tool.

The code for handling these analyses and collecting the results are much more complex than a loop. In the literature, Andrubis [START_REF] Lindorfer | ANDRUBIS -1,000,000 Apps Later: A View on Current Android Malware Behaviors[END_REF] was one of the most complex developed framework that handles multiple analyses on large volume of applications. They were able to achieve 3,500 analyses per day. Andlantis [START_REF] Bierma | Andlantis: Large-scale android dynamic analysis[END_REF] is another solution using 200 computing nodes, with very high throughput and scalability. Most of the time, researchers that have developed software for coordinating multiple analyses, do not share the code [START_REF] Bierma | Andlantis: Large-scale android dynamic analysis[END_REF], [START_REF] Lindorfer | ANDRUBIS -1,000,000 Apps Later: A View on Current Android Malware Behaviors[END_REF], except few tools, like the IRMA framework 1 . Additionally, this code have precise hardware requirements i.e. multiple physical servers that enables to have high performance throughput. These solutions cannot be used when prototyping experiments and are only useful for production time.

In this paper we present the PyMaO 2 (Python Malware Orchestrator), a tool for orchestrating an experiment on a regular PC desktop. An experiment is a sequence of analyses. Each analysis can depend on other ones and have pre-conditions authorizing its run. An experiment is robust to crashes of the tool (results are not lost) or to crashes of the smartphones that are used by dynamic analyses.

II. SOLVED CHALLENGES

Prototyping software for malware analysis requires to test methodologies with a dataset containing enough material for triggering special cases that can reveal some bugs. When manipulating a smartphone or an emulator, the execution of malicious software may damage the operating system, requiring to restore the used device. As a consequence, any error should be clearly reported to the user for further investigation. If our tool crashes, it should be able restart itself and to take into account that some results have been previously computed and should not be done again. In our tool, this is achieved using a JSON representation of the results of all analyses that is reloaded if the tool have to evaluate again an APK file.

Moreover, the tool brings simplicity when crafting new experiments and performances at execution time. This is achieved by coding each analysis as an independent class and by combining these analyses with pre-conditions authorizing the execution of each of them. At runtime, multiple workers use all the available CPU threads and manipulate the uncompressed data directly into the RAM memory.

III. ORCHESTRATOR ARCHITECTURE AND USAGE

A. Overview

Figure 1 depicts an overview of the architecture of PyMaO. This tool receives a set of APKs and an experiment to conduct on each APK file. The experiment is composed by a sequence of multiple analyses. An analysis is launched, for a given APK, if all its dependencies have already been launched and if its associated conditions are met. An example of an experiment is given in Section III-B. All these requirements are handled by the producer which is in charge of dispatching the analyses' run to the workers. Each worker is executed on a separate thread. When a worker finishes an analysis, it updates the JSON file corresponding to the analyzed APK. Finally, all the JSONs are processed by the reporter. This part is described in Section III-C.

When performing a dynamic analysis, a worker can uses a real smartphone. To avoid concurrency issues, each worker has a dedicated device. Because running malware on a smartphone may crash the smartphone, a watchdog thread has been implemented, which continuously receives heartbeats sent by a homemade software installed on every phone. If the watchdog does not receive a heartbeat, it reboots and restores the crashed phone to an initial state.

B. Declaring chains of analysis

PyMaO has been developed with usability in mind. Thus, developing new experiments that use external tools is simple. Listing 1 contains all the required code, except few import statements, to create a fully working experiment. All the remaining information is contained in the super class Experiment (line 1). The created experiment first runs APKiD 3 , a tool that detects packers artifacts (line 3). Then, if APKiD has correctly run (condition line 5), it parses its output using the Packer analysis (line 4). Finally, if the usage of a packer has been detected (line 7), the experiment installs (line 6). If this install succeeded (line 9), the tool launches the APK and checks its liveness (line 8). By dividing analyses in unitary operations, PyMaO avoids to copy past these functionalities for new designed experiments.

C. Reporting results

After executing an experiment, the tool can extract an aggregated information from the JSON files. We developed two post processing scripts generating two types of results. First, the tool can generate tables for counting features in the JSON files and generate ratios. For example, the table can report the number of detected malware if the experiment is a detection algorithm. Second, the tool can draw charts for reporting the usage of a feature in the dataset. For example, Figure 2 is an extract of an experiment conducted previously on the GM19 dataset [START_REF] Viet Triem | Isolating malicious code in android malware in the wild[END_REF], that shows the top most used methods on 5000 goodware and 5000 malware.

IV. FUTURE WORK

Fig. 1 .

 1 Fig. 1. Architecture overview

Fig. 2 .

 2 Fig.2. Top 10 most used API methods by malware in relation to goodware[START_REF] Viet Triem | Isolating malicious code in android malware in the wild[END_REF]

We continue to enhance the tool with new functionalities. For example, the resource usage (CPU, devices, memory) can be handled more accurately. By evaluating the profile of each analysis, the workers can choose the best task to achieve with the current remaining amount of resources available. Another future work concerns the generation of subsets of datasets with a descriptive language requesting the wanted features.


MD, PhD Loïc Sentilhes
email: loicsentilhes@hotmail.com

MD, PhD Gilles Kayem

MD Robert Silver

Prof Loïc Sentilhes

Conservative management of placenta accreta spectrum

Keywords: placenta accreta spectrum, morbidly adherent placenta, abnormally invasive placenta, placenta percreta, conservative management, leaving placenta in situ

The purpose of this review is to assist obstetricians-gynaecologists in considering the most appropriate conservative treatment option to manage women with placenta accreta spectrum according to their individual need and local expertise of the heath care team. The issue is challenging since the quality of evidence regarding efficacy is poor and is

Introduction

Conservative management of placenta accreta is defined as all procedures or strategies aiming to avoid a peripartum hysterectomy and its related-morbidity and consequences. The main goals are to decrease severe maternal morbidity related to the placenta accreta spectrum, especially the amount of blood loss; and consequently the risk of massive transfusion and coagulopathy as well as operative injury and its potential consequences such as vesicouterine fistula. A second goal may be to attempt to preserve the option of future pregnancies, knowing that fertility is often inextricably linked with societal status and self-esteem. Four types of conservative management have been described; extirpative treatment [START_REF] Kayem | Conservative versus extirpative management in cases of placenta accreta[END_REF], expectant management or the leaving placenta in situ [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF], one-step conservative surgery [START_REF] Palacios-Jaraquemada | Anterior placenta percreta: surgical approach, hemostasis and uterine repair[END_REF] and the triple-P procedure [START_REF] Viñas | Prevention of postpartum hemorrhage and hysterectomy in patients with morbidly adherent placenta: a cohort study comparing outcomes before and after introduction of the Triple-P procedure[END_REF]. For each of these procedures, there is only low quality evidence available derived from retrospective case series. .

The extirpative approach

The concept of this approach is simple; the aim is to avoid leaving retained placental tissue in the uterine cavity. Retained placenta is a common cause of postpartum hemorrhage and complete removal decreases the risk of bleeding [START_REF] Sentilhes | Postpartum haemorrhage: prevention and treatment[END_REF][START_REF] Sentilhes | Postpartum Hemorrhage: Guidelines for clinical practice from the French College of Gynaecologists and Obstetricians (CNGOF) in collaboration with the French Society of Anesthesiology and Intensive Care (SFAR)[END_REF]. Therefore, the procedure consists of manually removing the placenta to obtain an "empty" uterus. Unfortunately, in cases of placenta accreta spectrum (PAS), this procedure often results in massive hemorrhage. Kayem et al. performed a retrospective study comparing two consecutive epochs. In the first one, the extirpative approach was routinely applied for PAS whereas in the second one, the placenta was left in situ. Mean number of red blood cells (RBC) transfused (3,230 ± 2,170 mL versus 1,560 ± 1,646 mL; p < .01), disseminated intravascular coagulation (5 [38.5%] versus 1 [5.0%]; p=02), and hysterectomy rates (11 [84.6%] versus 3 [15%]; p < .001), were reduced using the placenta in situ approach [START_REF] Kayem | Conservative versus extirpative management in cases of placenta accreta[END_REF]. Moreover, when a cesarean-hysterectomy for suspicion of PAS has been planned, Eller et al. showed that early maternal morbidity was increased when placental removal was attempted compared with the placenta left undisturbed in situ (67% versus 36%; p = 0.04) [START_REF] Eller | Optimal management strategies for placenta accreta[END_REF]. Consequently, several authorities recommend that manual placental removal should be avoided in cases of planned cesarean-hysterectomy [START_REF]Society for Maternal-Fetal Medicine1, Belfort MA. Placenta accreta[END_REF][START_REF]Committee opinion No. 529: placenta accreta[END_REF][START_REF] Rcog | Placenta praevia, placenta praevia accreta and vasapraevia: diagnosis and management[END_REF][START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF]. The downside of this approach is the potential for unnecessary hysterectomy if the patient does not really have PAS. In conclusion, extirpative approach with a forcible manual removal of the placenta should be abandoned unless there is a low probability of PAS [START_REF] Sentilhes | Management of placenta accreta[END_REF].

Unfortunately, manual removal of the placenta usually happens in most cases with undiagnosed placenta accreta. In our opinion, women with strongly suspected PAS should never have attempted manual removal of the placenta. For women with risk factors for PAS or mild suspicion of PAS, caregivers should stop attempts to manually remove the placenta in cases of unusual and unexplained difficulties before the occurrence of massive hemorrhage.

Leaving placenta in situ without hysterectomy or expectant management

Short-and mid-term maternal outcome

This approach consists of leaving the placenta in situ and waiting for complete resorption. It was first described mainly in France [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF] and initially was termed 'conservative treatment of placenta accreta'. As other conservative approaches have been since described, it is more accurate to use the term 'leaving the placenta in situ without hysterectomy' or 'expectant management' [START_REF] Fox | Conservative management of morbidly adherent placenta: expert review[END_REF].

The goals of this approach are to avoid the morbidity associated with hysterectomy, preserve fertility and still avoid hemorrhage. Planned cesarean-hysterectomy while leaving the placenta in situ is considered the "gold standard" treatment for PAS [START_REF] Sentilhes | Postpartum Hemorrhage: Guidelines for clinical practice from the French College of Gynaecologists and Obstetricians (CNGOF) in collaboration with the French Society of Anesthesiology and Intensive Care (SFAR)[END_REF][START_REF] Eller | Optimal management strategies for placenta accreta[END_REF][START_REF]Society for Maternal-Fetal Medicine1, Belfort MA. Placenta accreta[END_REF][START_REF]Committee opinion No. 529: placenta accreta[END_REF][START_REF] Rcog | Placenta praevia, placenta praevia accreta and vasapraevia: diagnosis and management[END_REF][START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF][START_REF] Sentilhes | Management of placenta accreta[END_REF] but is associated with high rates of severe maternal morbidity (40% to 50% [START_REF] Sentilhes | Management of placenta accreta[END_REF]) and loss of fertility. Cesarean hysterectomy with placenta percreta is even more morbid, with reported mortality rates up to 7% [START_REF] O'brien | The management of placenta percreta: conservative and operative strategies[END_REF]. By leaving the adherent placenta in situ after the delivery of the child, one can expect a significant decrease of blood flow within the uterus and even the parametrium. This also will occur within the placenta, and the placenta will progressively and spontaneously detach from the uterus and even adjacent organs by necrosis. It is analogous to cutting the foot of ivy that is incrusted into a stone wall, and waiting for its death before removing it in order to avoid weakening the wall. This approach is particularly attractive for severe PAS with adjacent organ invasion in order to avoid operative complications and injuries.

On the other hand, expectant management has important risks. These include intrauterine infection, placental abscess and even sepsis, as well as unpredictable massive hemorrhage.

Moreover, it requires long-term monitoring until complete resorption of the placenta.

In practice, the exact position of the placenta is determined by a preoperative ultrasound.

Before initiating cesarean delivery, all materials required for an immediate conversion to hysterectomy are readily available. Laparotomy is made by a midline vertical cutaneous incision, often enlarged above the umbilicus. The uterine approach uses a midline or "classical" incision at a distance from the placental bed. After delivery of the child, and only in cases wherein PAS is unlikely, the obstetrician carefully attempts to remove the placenta by controlled cord traction (see below); If the placenta does not easily separate form the uterus, it confirms the diagnosis of MAP. In this case, the cord is tied with suture, cut at the site of insertion and the uterine cavity is closed. Postoperative antibiotic therapy (amoxicillin and clavulanic acid) is usually administered prophylactically for 5 days to minimize the risk of infection, although efficacy is uncertain. Adjunctive procedures (embolization or vessel ligation, temporal internal iliac occlusion balloon, methotrexate, hysteroscopic resection of retained tissues) may be used to attempt to decrease morbidity or to hasten placental resorption. As with antibiotic treatment, none of these interventions is proven to improve outcomes.

In France, the first conservative treatment took place in 1993; the number of procedures increased steadily, particularly during the 2000's [START_REF] Viñas | Prevention of postpartum hemorrhage and hysterectomy in patients with morbidly adherent placenta: a cohort study comparing outcomes before and after introduction of the Triple-P procedure[END_REF]. First, only very limited data about maternal outcome after conservative management were available. Moreover, they were from small case reports and case series from individual tertiary-care institutions [START_REF] Kayem | Conservative versus extirpative management in cases of placenta accreta[END_REF][START_REF] Sentilhes | Management of placenta accreta[END_REF].

In 2007, Timmermans et al. reviewed available case series of placenta accreta managed by leaving the placenta in situ [START_REF] Timmermans | Conservative management of abnormally invasive placentation[END_REF]. They found 48 case reports describing the outcome of 60 women as well as two French case series including 31 women, yielding available data on 91 cases. Of the 26 women managed conservatively while leaving the placenta in situ without the use of additional therapies, 22 (85%) had a favorable outcome. Expectant management failed in 4 (15%) of patients who required hysterectomy due to severe hemorrhage or infection [START_REF] Timmermans | Conservative management of abnormally invasive placentation[END_REF].

In order to increase statistical power and satisfactory external validity, a French multicenter retrospective study was conducted to determine maternal outcome after conservative treatment [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Of 45 university hospitals in France, 40 (88.9%) agreed to participate in the study, and 25 used conservative treatment for placenta accreta at least once.

Placenta accreta was diagnosed according to the following clinical and histologic criteria: 1) It was partially or totally impossible to manually remove the placenta with no discernable cleavage plane between all or part of the placenta and uterus, 2) prenatal diagnosis of placenta accreta on sonogram, confirmed by the failure of gentle attempts to remove it during the third stage of labor or at cesarean delivery, 3) evidence of placental invasion at the time of surgery; 4) histologic confirmation of accreta on hysterectomy specimen. Women treated with an extirpative approach or a planned cesarean-hysterectomy were excluded from this study.

Conservative management in case of placenta accreta was defined by the decision of the obstetrician to leave the placenta partially or totally in situ, with no attempt to remove it forcibly. When placenta accreta was not suspected before delivery, it was diagnosed when it was impossible to detach the placenta by gentle manipulation, and conservative treatment was defined as leaving part or all of it in the uterus. The study included 167 cases of placenta accreta with 59% of placentas left partially in situ and 41% left totally in situ. Outcomes are summarized in Table 1 [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Success rates were similar to prior reports [START_REF] Kayem | Conservative versus extirpative management in cases of placenta accreta[END_REF][START_REF] Sentilhes | Management of placenta accreta[END_REF] with successful uterine preservation (no hysterectomy) in 78.4% of cases. Importantly, severe maternal morbidity occurred in only 6% (10/167) (defined as any of the following: sepsis, septic shock, peritonitis, uterine necrosis, postpartum uterine rupture, fistula, injury to adjacent organs, acute pulmonary edema, acute renal failure, deep vein thrombophlebitis or pulmonary embolism, or maternal death) [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. One maternal death related to multi-organ failure occurred in a patient with marrow aplasia, nephrotoxicity with acute renal failure, followed by peritonitis with septic shock, after injection of methotrexate in the umbilical cord. Other rare morbidities included vesico-vaginal fistula and arteriovenus fistula formation. These complications also have been reported by others [START_REF] Sentilhes | Management of placenta accreta[END_REF][START_REF] Fox | Conservative management of morbidly adherent placenta: expert review[END_REF] and are similar to those reported after planned cesarean hysterectomy [START_REF] Eller | Optimal management strategies for placenta accreta[END_REF][START_REF]Society for Maternal-Fetal Medicine1, Belfort MA. Placenta accreta[END_REF][START_REF] Rcog | Placenta praevia, placenta praevia accreta and vasapraevia: diagnosis and management[END_REF].

The placenta spontaneously and completely resorbed in 75% of cases after a median of 13.5 weeks (min: 4 weeks, max: 60 weeks). Hysteroscopic resection and / or curettage were performed to remove any remaining placenta in 25% at a median of 20 weeks after delivery (min: 2 weeks, max: 45 weeks) [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Strengths of this retrospective study included a large number of cases and participating centers, which increases the study's external validity. Thus, it is reasonable to anticipate similar results in other University teaching hospitals that may have limited experience in conservative treatment of placenta accreta, but where blood banks, pelvic arterial embolizations, obstetric subspecialties, obstetric anesthesia, interventional radiology, urology, and gynecological oncology are readily available.

Limitations include its retrospective design and the absence of histologic confirmation of PAS in cases without hysterectomy [START_REF] Silver | Placenta Accreta Spectrum[END_REF]. Accordingly, some of these cases may not truly have been PAS, resulting in possible bias and underestimation of maternal morbidity associated with conservative management. Indeed, only about half of women had a placenta previa and prenatal suspicion of PAS, and the rate of previous cesarean was lower than in other series [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF][START_REF] Silver | Placenta Accreta Spectrum[END_REF]. It is noteworthy that conservative management was typically proposed to women who desired further pregnancies [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF][START_REF] Sentilhes | Management of placenta accreta[END_REF]. This may account for the characteristics of the population, wherein only 53% of women had a previous cesarean but 96% had at least one risk factor. Moreover, we used stringent and uniformly applied criteria to define PAS (see above) in order to minimize this limitation. Finally, histopathological examination confirmed the diagnosis of placenta accreta in all immediate (18/18) and all but one delayed hysterectomies (17/18) [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Despite these reassuring elements regarding possible selection bias, we acknowledge that such bias may exist, and that some women may not have had PAS.

Indeed, the problem of being certain of PAS concerns all studies related to placenta accreta/increta/percreta when no hysterectomy specimen for histopathologic confirmation is available. Consequently, assessment of conservative management of PAS is difficult. In a review detailing correlations between ultrasound and pathological findings, only 72/1078 cases had histopathological descriptions [START_REF] Jauniaux | Accreta placentation: a systematic review of prenatal ultrasound imaging and grading of villous invasiveness[END_REF].

Data are even more scarce regarding conservative management of placenta percreta.

Pather et al. reported three cases of placenta percreta treated with conservative management and also performed a review of available data. They found 57 cases of suspected placenta percreta that were managed conservatively with the placenta left in situ. Hysterectomy was avoided in 60% of cases and 42% experienced major morbidity (including sepsis, coagulopathy, hemorrhage, pulmonary embolism, fistula and arteriovenous malformation) [START_REF] Pather | Maternal outcome after conservative management of placenta percreta at caesarean section: a report of three cases and a review of the literature[END_REF]. In a similar review, Clausen et al retrieved 36 cases of placenta percreta managed by leaving the placenta in-situ [START_REF] Clausen | Management of placenta percreta: a review of published cases[END_REF]. Delayed hysterectomy was required in 58% of cases. In the French national study that reported the largest series of consecutive cases of placenta percreta with attempt to leave the placenta in situ (n=18), prenatal diagnosis by ultrasonography or MRI was performed in 14 cases and during labor (at the time of the cesarean) in four cases [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Conservative treatment was successful for 10 of 18 cases (55.6%) of placenta percreta, and severe maternal morbidity occurred in 3 of the 18 (16.7%). Of the eight cases of placenta percreta with bladder involvement, conservative treatment was successful in six cases (75%) and severe maternal morbidity occurred in two (25%) [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Although morbidity was considerable, it was favorable in comparison with planned cesarean-hysterectomy in women with percretas [START_REF] O'brien | The management of placenta percreta: conservative and operative strategies[END_REF].

These results show that leaving placenta in situ is a reasonable option for women with PAS who are properly counseled and motivated, in particular if they desire future pregnancies. It also is critical that they agree to close follow-up monitoring in centers with adequate equipment and resources [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF][START_REF] Sentilhes | Postpartum Hemorrhage: Guidelines for clinical practice from the French College of Gynaecologists and Obstetricians (CNGOF) in collaboration with the French Society of Anesthesiology and Intensive Care (SFAR)[END_REF][START_REF]Society for Maternal-Fetal Medicine1, Belfort MA. Placenta accreta[END_REF][START_REF]Committee opinion No. 529: placenta accreta[END_REF][START_REF] Rcog | Placenta praevia, placenta praevia accreta and vasapraevia: diagnosis and management[END_REF][START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF]. However, many questions remain unanswered because only scare data are available regarding the various adjunctive treatments and procedures used in a conservative approach with the placenta left in situ:

Gentle attempted removal of the placenta

There are few data available to answer this question. The main drawback of attempted removal of the placenta is that this procedure can cause severe bleeding with a risk of maternal hemorrhagic complications and hysterectomy. Its main advantage is to potentially avoid leaving an in situ placenta, if there is not really PAS, as well as to remove the nonadherent portion of the placenta when the placenta adheres partially to the myometrium. This can reduce the volume of placenta left in the uterus, potentially reducing the risk of bleeding and infection. It is important to emphasize imprecision in the antenatal diagnosis of PAS using Doppler ultrasound and/or MRI. These two imaging modalities are good but imperfect for the diagnosis of PAS [START_REF] Sentilhes | Management of placenta accreta[END_REF][START_REF] Kayem | PACCRETA: clinical situations at high risk of placenta ACCRETA/percreta: impact of diagnostic methods and management on maternal morbidity[END_REF]. The consequences of a false-negative result are obvious, i.e. increased maternal morbidity [START_REF] Sentilhes | Management of placenta accreta[END_REF]. Similarly, caregivers should be aware that false-positive results, which may occur in up to 28% of cases [START_REF] Eller | Optimal management strategies for placenta accreta[END_REF], also increase maternal morbidity. They may lead caregivers to perform unnecessary surgical procedures with their inherent complications. It makes sense to consider the context. Thus, our current practice is to attempt to gently remove the placenta by cord traction only in cases when the diagnosis of placenta accreta is uncertain. An example would be a nulliparous woman with a history of curettage in whom ultrasound revealed intraplacental lacunae in a low-lying anterior placenta and no visible evidence of placenta accreta during the cesarean [START_REF] Sentilhes | Management of placenta accreta[END_REF].

Methotrexate (MTX) adjuvant treatment

Some authors have proposed the use of methotrexate to hasten placental resolution [START_REF] Mussalli | Placenta accreta and methotrexate therapy: three case reports[END_REF]. Its efficacy for this indication has never been demonstrated and only case reports and small case series with no control groups have been reported [START_REF] Timmermans | Conservative management of abnormally invasive placentation[END_REF]. Accordingly, the Royal College of Obstetricians and Gynaecologists (RCOG) as well as the International Federation of Gynecology and Obstetrics (FIGO) do not recommend its routine use [START_REF] Rcog | Placenta praevia, placenta praevia accreta and vasapraevia: diagnosis and management[END_REF][START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF]. The low rate of placental cell division in the third trimester compared to early pregnancy raises the question of whether methotrexate has any effect on placental resorption. In addition, methotrexate can rarely cause serious harm such as neutropenia or medullary aplasia, even with a single dose in a young patient [START_REF] Sentilhes | Management of placenta accreta[END_REF]. These complications are particularly morbid in the setting of infection, which is one of the more common complications of conservative management [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Finally, the only case, to our knowledge of maternal death after conservative treatment was secondary to a cascade of complications (bone marrow suppression, sepsis, renal failure) attributed to an intra-umbilical cord administration of methotrexate [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. For these reasons, we do not advocate the use of methotrexate in cases of conservative treatment.

Prophylactic surgical or radiological uterine devascularization

There are also very limited data on the use of these adjuvant techniques. Prophylactic devascularization can be achieved by techniques used to treat postpartum hemorrhage (embolization, bilateral uterine artery ligation, stepwise uterine devascularization, bilateral ligation of hypogastric arteries), although these uterine-sparing procedures may be relatively less effective in cases of placenta accreta [START_REF] Sentilhes | Fertility and pregnancy outcomes following uterine devascularization for severe postpartum haemorrhage[END_REF][START_REF] Sentilhes | Predictors of failed pelvic arterial embolization for severe postpartum hemorrhage[END_REF]. Angstmann et al. demonstrated that prophylactic embolization before performing cesarean hysterectomy may reduce the risk of blood loss with accreta [START_REF] Angstmann | Surgical management of placenta accreta: a cohort series and suggested approach[END_REF]. Thus, it is possible that prophylactic devascularization could reduce the risk of secondary hemorrhage in the setting of conservative treatment [START_REF] Bouvier | Planned caesarean in the interventional radiology cath lab to enable immediate uterine artery embolization for the conservative treatment of placenta accreta[END_REF]. It could also theoretically accelerate placental resolution. In fact, in a retrospective comparative study, the median delay for complete placental resorption was significantly shorter when women underwent an embolization (median=17 weeks; q 1 011.5; q 3 023; range: 1-38 weeks) compared to women who did not undergo embolization (median=32 weeks; q 1 018; q 3 048.8; range: 12-111 weeks) (P=0.036). Unfortunately, the reason for embolization was not clearly reported by the authors [START_REF] Bouvier | Planned caesarean in the interventional radiology cath lab to enable immediate uterine artery embolization for the conservative treatment of placenta accreta[END_REF]. In contrast, devascularization may cause harm [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF][START_REF] Sentilhes | Predictors of failed pelvic arterial embolization for severe postpartum hemorrhage[END_REF]. In the French multicenter series of 167 cases of placenta accreta treated conservatively, the only two cases of uterine necrosis occurred in patients (62 total) who underwent arterial embolization [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF].

Other adverse effects of uterine artery embolization also have been reported [START_REF] Sentilhes | Management of placenta accreta[END_REF]. The risk:benefit ratio of routine devascularization procedures in conservative management of placenta accreta remains to be determined.

Monitoring of conservative management

Unfortunately, there are no data regarding this important issue. In our practice, we typically observe the patient in the hospital for up to 8 days and administer prophylactic antibiotics for 5 days. This epoch is the time of highest risk for bleeding and infection. Prior to discharge, the woman and her partner should be advised about the need for close, long-term monitoring.

There is still a risk for bleeding and infection and the size and vascularization of the retained placenta often does not meaningfully change for several weeks. The following symptoms require emergency medical attention: hyperthermia, severe pelvic pain, foul smelling vaginal discharge, and bleeding. She also should be advised about the possibility of abnormal and persistent vaginal discharge. There should be a multidisciplinary team available with the skills to manage complications twenty-four hours a day, seven days a week [START_REF] Sentilhes | Management of placenta accreta[END_REF][START_REF] Silver | Center of excellence for placenta accreta[END_REF]. Patients are seen for outpatient clinic visits weekly for the first two months. If she is asymptomatic, monthly visits are conducted until complete resorption of the placenta. The visits include a clinical examination (bleeding, temperature, pelvic pain), pelvic ultrasound (size of retained tissue) and laboratory screen for infection (hemoglobin and leukocytes, C reactive protein, vaginal sample for bacteriological analysis.) [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. Of course, the efficacy of most of these measures is uncertain, but in theory they may reduce the risk of serious complications.

We do not routinely use magnetic resonance (MRI) imaging and serial beta human chorionic gondadotropin (HCG) levels for monitoring. Soyer et al. used MRI to follow 23 women with placenta left in situ for PAS [START_REF] Soyer | Placental vascularity and resorption delay after conservative management of invasive placenta: MR imaging evaluation[END_REF]. The median delay for complete placental resorption was 21.1 weeks (1-111). They found a significant correlation between the degree of vascularity on early phase of dynamic MRI and delay of complete placental resorption (r=0.69; P<.001). They speculate that MRI may help predict delay for complete placental resorption [START_REF] Soyer | Placental vascularity and resorption delay after conservative management of invasive placenta: MR imaging evaluation[END_REF]. It is not clear whether decreasing levels of βhCG correlate with the rate of involution of placental tissue. Khan et al and Torrenga and colleagues described several cases of placenta left in situ followed with serial beta HCG levels [START_REF] Khan | Conservative management of morbidly adherant placenta -a case report and review of literature[END_REF][START_REF] Torrenga | Postpartum monitoring of retained placenta. Two cases of abnormally adherent placenta[END_REF]. Serum beta HCG levels decreased to minimal levels in five months in the Khan study and in in 5 to 10 weeks in the Torrenga study. In both studies, beta HCG levels did not correlate with the volume of remaining tissue [START_REF] Khan | Conservative management of morbidly adherant placenta -a case report and review of literature[END_REF][START_REF] Torrenga | Postpartum monitoring of retained placenta. Two cases of abnormally adherent placenta[END_REF], raising questions about its usefulness for the monitoring of these patients. Thus, measuring serum beta hCG on a weekly basis can reassure to some extent, but low levels do not guarantee complete placental resolution [START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF]. Consequently, placental resorption should be documented by ultrasound imaging [START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF].

Systematic hysteroscopic resection of placental tissue that does not resorb.

Again, data regarding this issue are scarce. As mentioned previously in the French retrospective study, hysteroscopic resection or curettage or both were used to remove retained placenta in 29 (25.0%) cases, at a median of 20 weeks (range 2-45 weeks) after delivery [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF].

These results highlight the fact that this procedure is performed frequently. Nevertheless, no information regarding the reason for performing this procedure (due to pain, bleeding and or infection, to hasten placental resorption, on maternal request or systematically) was available.

In a small cohort of 23 women with placenta left in situ for placenta accreta, 12 underwent hysteroscopy under ultrasound guidance due to pain and/or bleeding with retained placental tissue [START_REF] Legendre | Conservative management of placenta accreta: hysteroscopic resection of retained tissues[END_REF]. The use of bipolar energy was limited as much as possible to minimize risk of uterine perforation. The median size of the retained placenta was 54mm . No complications occurred due to hysteroscopic resection. Complete removal (11/12) was achieved after one, two and three hysteroscopic procedures in 5 (41.7%), 2 (16.7%) and 4 (33.3%) cases, respectively. One delayed hysterectomy was performed after "failure" of the hysteroscopic procedure [START_REF] Legendre | Conservative management of placenta accreta: hysteroscopic resection of retained tissues[END_REF]. It seems that hysteroscopic resection may shorten recovery time without harmful effects in symptomatic women. The role of prophylactic hysteroscopy or the timing of it in asymptomatic women is unknown. The safety and feasibility of high-intensity focused ultrasound (HIFU) in the treatment of placenta accreta after vaginal delivery was recently tested in 12 women with placenta accreta [START_REF] Bai | High-intensity focused ultrasound treatment of placenta accreta after vaginal delivery: a preliminary study[END_REF]. The average period of residual placental involution was 36.9 days. HIFU treatment did not apparently increase the risk of infection or hemorrhage and no patient required hysterectomy.

Delayed interval hysterectomy

Another possible advantage of leaving the placenta in situ is to plan a delayed interval hysterectomy, after partial involution of the placenta and decreased uterine vascularity. This may decrease hemorrhagic morbidity and risk of injury to adjacent organs. This strategy seems most attractive in women with placenta percreta, who are at highest risk for blood loss and urinary tract injury. Excellent outcomes have been reported using this approach in percreta cases [START_REF] Lee | Medical and surgical treatment of placenta percreta to optimize bladder preservation[END_REF]. On the other hand, this approach requires two surgeries instead of one and both may be quite morbid. Also, there is a risk of hemorrhage or infection prompting the need for emergency hysterectomy during the planned interval. Finally, the optimal timing of planned delayed hysterectomy is uncertain [START_REF] Fox | Conservative management of morbidly adherent placenta: expert review[END_REF]. It may only be possible to truly ascertain whether delayed interval hysterectomy is effective through appropriate randomized clinical trials.

Long-term maternal outcome and subsequent fertility and obstetrical outcome

Few data are available regarding subsequent pregnancies in women with conservative management of PAS using the placenta in situ approach, but successful pregnancies have been reported [START_REF] Sentilhes | Management of placenta accreta[END_REF]. However, these reports are biased towards successful outcomes.

Therefore, an attempt was made to contact all women included in the French national retrospective study who did not undergo a hysterectomy, to estimate fertility and pregnancy outcomes after successful expectant management [START_REF] Sentilhes | Fertility and pregnancy outcomes following uterine devascularization for severe postpartum haemorrhage[END_REF]. Follow-up data were available for 96 (73.3%) of the 131 women included in the study. There were eight women who had severe intrauterine synechiae and were amenorrheic. Of the 27 women who reported wanting more children, 3 women were attempting to become pregnant (mean duration: 11.7 months, range: 7-14 months), and 24 (88.9%) women had had 34 pregnancies (21 third-trimester deliveries, 1 ectopic pregnancy, 2 elective abortions and 10 early pregnancy losses) with a mean time to conception of 17.3 months (range, 2-48 months). All 21 deliveries resulted in healthy babies born after 34 weeks of gestation. Placenta accreta recurred in 6 of 21 cases (28.6%) and was associated with placenta previa in 4 cases. Postpartum hemorrhage occurred in four (19%) cases; this was associated with PAS in three and to uterine atony in one. These results show that successful expectant management for placenta accreta can be associated with successful subsequent fertility and pregnancy, although there is an increased risk of recurrent PAS [START_REF] Sentilhes | Fertility and pregnancy outcomes following uterine devascularization for severe postpartum haemorrhage[END_REF].

Planned cesarean-hysterectomy versus conservative treatment

This is one of the most important unresolved questions regarding the management of PAS. However, there is only one small retrospective study directly comparing maternal outcomes following planned cesarean-hysterectomy (n=16) versus conservative management while leaving the placenta in situ (expectant management) (n=10) [START_REF] Jolley | Management of placenta accreta: a survey of Maternal-Fetal Medicine practitioners[END_REF]. No differences were observed between groups except for estimated blood loss, which was lower in the conservative treatment group (3625mL ± 2154 versus 900mL ± 754; p< .05) [START_REF] Jolley | Management of placenta accreta: a survey of Maternal-Fetal Medicine practitioners[END_REF]. Of course this study was too small and prone to bias to truly compare strategies. In fact, it is possible that severe maternal morbidity is increased in cases of conservative treatment because unpredictable infectious complications, uterine necrosis and secondary hemorrhage associated with conservative treatment can be dramatic. As with delayed interval hysterectomy, the relative merits of planned cesarean hysterectomy and conservative management will only be elucidated through properly designed clinical trials.

Until such trials are completed, it seems reasonable to counsel women about planned cesarean hysterectomy and conservative management. A major consideration is whether or not future childbearing is desired. A planned cesarean-hysterectomy may be the best option if the patient has no desire for more children, is older and / or multiparous. Nevertheless, we believe that conservative management is a reasonable option for patients who are properly counseled and motivated. For example, women who want the option of future pregnancies, who agree to close follow-up monitoring, and who are in centers with adequate equipment and resources [1-2, 6, 11-12].

Moreover, leaving the placenta in situ may prove to be the most appropriate choice in the most severe cases of PAS, in particular in cases of organ adjacent invasion [START_REF] Sentilhes | Management of placenta accreta[END_REF], where radical surgery is often associated with severe maternal morbidity [START_REF] O'brien | The management of placenta percreta: conservative and operative strategies[END_REF]. Others also favor this approach, even in the U.S. where conservative management is less common than in France.

An U.S. survey noted that 14.9% of providers would attempt to leave the placenta in situ in a hemodynamically stable patient [START_REF] Jolley | Management of placenta accreta: a survey of Maternal-Fetal Medicine practitioners[END_REF] and 32% had attempted conservative management for PAS [START_REF] Esakoff | PAMUS: placenta accreta management across the United States[END_REF].

One step-conservative surgery

This is an alternative conservative procedure that has been described by one author [START_REF] Palacios-Jaraquemada | Anterior placenta percreta: surgical approach, hemostasis and uterine repair[END_REF]. It consists of resecting the invaded area of the uterus together with the placenta and reconstructing the uterus. It is performed at the time of cesarean delivery as a "one-step procedure" [START_REF] Palacios-Jaraquemada | Anterior placenta percreta: surgical approach, hemostasis and uterine repair[END_REF]. This strategy aims to combine the advantages of the leaving the placenta in situ approach (i.e. preserving fertility) and of cesarean-hysterectomy (no persistent high risk of bleeding or infection after the procedure). The main steps of this uterine-sparing technique achieved through a median or Pfannenstiel incision are (1) vascular disconnection of newlyformed vessels and the separation of invaded uterine from invaded vesical tissues; [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF] performance of an upper-segmental hysterotomy; (3) resection of all invaded tissue and the entire placenta in one piece; (4) use of surgical procedures for hemostasis; (5) myometrial reconstruction in two planes; [START_REF] Sentilhes | Postpartum Hemorrhage: Guidelines for clinical practice from the French College of Gynaecologists and Obstetricians (CNGOF) in collaboration with the French Society of Anesthesiology and Intensive Care (SFAR)[END_REF] bladder repair if necessary [START_REF] Palacios-Jaraquemada | Anterior placenta percreta: surgical approach, hemostasis and uterine repair[END_REF].

Palacios Jaraquemada et al. described outcomes of this one-step conservative surgery in 68 women presenting with placental invasion of adjacent organs (invasion of the posterior upper bladder (n=46; group 1), and of the posterior lower vesical area (n=22; group 2)) [START_REF] Palacios-Jaraquemada | Anterior placenta percreta: surgical approach, hemostasis and uterine repair[END_REF].

Uterine preservation was achieved in 95.7% (44/46) and 27.3% (6/22) of cases, respectively.

The indications for the 18 hysterectomies were segmental circumferential rupture greater than 50% (n=13), coagulopathy (n=2) infection (n=1) and uncontrolled hemodynamic instability (n=2). The following complications were reported (mostly in group 2): lower ureteral injuries (n=2), vesical fistula (n=1), hematoma in the vaginal cuff (n=1) and uterine infection (n=1).

Among the 50 women with uterine preservation, follow-up was available in 42. Menses were recovered between 3 and 16 months. Ten women had another uneventful pregnancy and delivery with no recurrence of PAS [START_REF] Palacios-Jaraquemada | Anterior placenta percreta: surgical approach, hemostasis and uterine repair[END_REF]. In another publication, Palacios Jaraquemada reported 45 pregnancies following a one step-procedure for placenta accreta [START_REF]Diagnosis and management of placenta accreta[END_REF]. Among these 45 pregnancies, 44 were uneventful and only one was complicated by a recurrence of PAS [START_REF]Diagnosis and management of placenta accreta[END_REF].

As we have limited experience with the one-step conservative surgery, we find it difficult to make strong recommendations regarding the technique. It is important to note that the one step procedure may be less reproducible and generalizable than conservative treatment because it requires a novel and specific surgical procedure. Successful use of the procedure by other groups and prospective trials will ultimately clarify the merits of one step conservative therapy.

The triple-P procedure

The team of Chandraharan proposed a novel uterine-sparing procedure for PAS termed "the triple-P procedure" [START_REF] Viñas | Prevention of postpartum hemorrhage and hysterectomy in patients with morbidly adherent placenta: a cohort study comparing outcomes before and after introduction of the Triple-P procedure[END_REF]. The main steps of this procedure include (i) preoperative placental localization using transabdominal ultrasound to identify the superior border of the placenta in order to deliver the fetus by an incision above the upper border of the placenta, (ii) pelvic devascularization involving preoperative placement of intra-arterial balloon catheters with inflation after delivery, and (iii) no attempt to remove the placenta with en bloc myometrial excision and uterine repair. It seems important to ensure that a 2-cm margin of myometrium is retained in the lower lip of the uterine incision to facilitate closure of the myometrial defect [START_REF] Viñas | Prevention of postpartum hemorrhage and hysterectomy in patients with morbidly adherent placenta: a cohort study comparing outcomes before and after introduction of the Triple-P procedure[END_REF]. Bleeding from the separated and adherent part of the placenta is controlled by over sewing the defect. If the posterior wall of the bladder is involved, placental tissue invading the bladder is left in situ to avoid cystotomy.

The authors reported a small series, comparing outcomes after (n=19) and prior to implementation of the Triple-P procedure (n=11). In the past, PAS was treated with an elective cesarean delivery, using an incision into the uterine fundus, leaving the placenta in part or entirely in the uterus unless PPH occurred and peripartum hysterectomy was required (control group) [START_REF] Viñas | Prevention of postpartum hemorrhage and hysterectomy in patients with morbidly adherent placenta: a cohort study comparing outcomes before and after introduction of the Triple-P procedure[END_REF]. Demographic characteristics were comparable between groups, with a percreta rate of 54.5% and 68.4% (p=.35), respectively. There was no statistical difference for the estimated mean blood loss (2,170 mL vs 1,700 mL; p=0.44) and the rate of transfusion (45.5% vs 47.4%; p=0.61). However, the rates of postpartum hemorrhage (54.5% vs 15.8%; p=0.035) and hysterectomy (27.3% vs 0.0%; p=0.045) were lower in the triple P group. One major complication (5%) occurred in a woman treated with triple P (right common iliac and external iliac artery thrombosis) [START_REF] Viñas | Prevention of postpartum hemorrhage and hysterectomy in patients with morbidly adherent placenta: a cohort study comparing outcomes before and after introduction of the Triple-P procedure[END_REF]. This is a known complication of temporal internal iliac occlusion balloon catheters [START_REF] Sentilhes | Management of placenta accreta[END_REF]. As with the one step procedure, these data should be considered preliminary and further studies are needed to assess relative efficacy. It is noteworthy that the RCOG and FIGO do not recommend balloons for cesarean-hysterectomy or conservative treatment [START_REF] Rcog | Placenta praevia, placenta praevia accreta and vasapraevia: diagnosis and management[END_REF][START_REF] Sentilhes | FIGO Placenta Accreta Diagnosis and Management Expert Consensus Panel. FIGO consensus guidelines on placenta accreta spectrum disorders: Conservative management[END_REF] due to untoward effects, although the issue remains controversial.

Conclusion

Except for extirpative treatment (best reserved for cases unlikely to be PAS), conservative management for PAS may be a reasonable alternative option to planned cesareanhysterectomy in well-selected cases. It is important that women treated with expectant management have appropriate counseling and close surveillance after delivery. The beststudied conservative approach is expectant care after leaving placenta in situ. Although comparable outcomes to planned cesarean hysterectomy have been reported, the approach is of uncertain efficacy due to bias in case selection and uncertainty regarding the diagnosis of PAS. Prospective trials are desperately needed to assess the true risks and benefits of conservative management overall, as well as for each approach. The prospective PACCRETA study has been initiated in order to answer some of the questions raised in this chapter [START_REF] Kayem | PACCRETA: clinical situations at high risk of placenta ACCRETA/percreta: impact of diagnostic methods and management on maternal morbidity[END_REF]. Table 1. Maternal morbidity after conservative treatment for placenta accreta, modified from Sentilhes et al. [START_REF] Sentilhes | Maternal outcome after conservative treatment of placenta accreta[END_REF]. 10 (6.0) Data presented as mean ± standard deviation, or as median with interquartile range in parentheses, or as number of patients with percentages in parentheses. * The total number of additional uterine devascularization procedures exceeds the number of patients because some patients had more than one such procedure. Some patients had more than one type of morbidity. † These two patients had bilateral supra-selective embolization of the uterine arteries due to primary postpartum hemorrhage on the day of delivery. Success of conservative treatment was defined as uterine preservation. A primary hysterectomy took place within the first 24 hours, whereas a delayed hysterectomy took place more than 24 hours after delivery.

Tables

Characteristics

Contribution to authorship

Loïc Sentilhes wrote the first draft of the report. All authors contributed to the writing of the final version and to its revision for important intellectual content, and all have seen and approved the final version.