[Lower Uterine Segment Trial: A pragmatic open multicenter randomized trial].

BACKGROUND: The data from literature show that trial of labor and elective repeat cesarean delivery after a prior cesarean delivery both present significant risks and benefits, and these risks and benefits differ for the woman and her fetus. The benefits to the woman can be at the expense of her fetus and vice-versa. This uncertainty is compounded by the scarcity of high-level evidence that preclude accurate quantification of the risks and benefits that could help provide a fair counseling about a trial of labor and elective repeat cesarean delivery. An interesting way of research is to evaluate the potential benefits of a decision rule associated to the ultrasound measurement of the lower uterine segment (LUS). Indeed, ultrasonography may be helpful in determining a specific risk for a given patient by measuring the thickness of the LUS, i,e, the thickness of the cesarean delivery scar area. Although only small and often methodologically biased data have been published, they look promising as their results are concordant: ultrasonographic measurements of the LUS thickness is highly correlated with the intraoperative findings at cesarean delivery. Furthermore, the thinner the LUS becomes on ultrasound, the higher the likelihood of a defect in the LUS. Finally, ultrasound assessment of LUS has an excellent negative predictive value for the risk of uterine defect. Therefore, this exam associated with a rule of decision could help to reduce the rate of elective repeat cesarean delivery and especially to reduce the fetal and maternal mortality and morbidity related to trial of labor after a prior cesarean delivery.

METHODS/DESIGN: This is a pragmatic open multicenter randomized trial with two parallel arms. Randomization will be centralized and computerized. Since blindness is impossible, an adjudication committee will evaluate the components of the primary composite outcome in order to avoid evaluation bias. An interim analysis will be planned mid-strength of the trial. Ultrasound will be performed by expert sonographers after certification by the main investigator. Women aged 18 years or older are eligible for this trial if they have a singleton pregnancy in cephalic presentation at a gestational age from 36 to 38 weeks, a previous low transverse cesarean delivery and sign the informed consent sheet. Women will be asked to participate in this study when they reach a term of 36 to 38 weeks of gestation. After agreement, women will be randomized into two groups: in the study group, they will have the LUS measured by ultrasound and the patient will be informed that, based on a threshold value of 3.5mm for the ultrasound measurement of the LUS thickness, the patient with a higher measurement will be considered at low risk and will be encouraged to choose a trial of labor whereas the patient with a measurement is equal to or less than this threshold will be considered at risk and encouraged to choose an elective repeat cesarean; in the control group, ultrasound LUS measurement will not be performed. The mode of delivery will be decided according to standard practice at the center. The primary composite outcome will include: uterine rupture, uterine dehiscence, hysterectomy, thromboembolic complications, transfusion, endometritis, maternal mortality, fetal prenatal and intrapartum mortality, hypoxic-ischemic encephalopathy and neonatal mortality.

DISCUSSION: This trial assesses the efficacy of ultrasound measurement of the lower uterine segment in women with a prior cesarean delivery in reducing fetal and maternal morbidity and mortality and it will provide evidence in order to establish clinical recommendations.

TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01916044 (date of registration: 5 August 2013).