The impact of manual rotation of the occiput posterior position on spontaneous vaginal delivery rate: study protocol for a randomized clinical trial (RMOS)

Background: The frequency of posterior presentations (occiput of the fetus towards the sacrum of the mother) in labor is approximately 20% and, of this, 5% remain posterior until the end of labor. These posterior presentations are associated with higher rates of cesarean section and instrumental delivery. Manual rotation of a posterior position in order to rotate the fetus to an anterior position has been proposed in order to reduce the rate of instrumental fetal delivery. No randomized study has compared the efficacy of this procedure to expectant management. We therefore propose a monocentric, interventional, randomized, prospective study to show the superiority of vaginal delivery rates using the manual rotation of the posterior position at full dilation over expectant management. Methods: Ultrasound imaging of the presentation will be performed at full dilation on all the singleton pregnancies for which a clinical suspicion of a posterior position was raised at more than 37 weeks' gestation (WG). In the event of an ultrasound confirming a posterior position, the patient will be randomized into an experimental group (manual rotation) or a control group (expectative management with no rotation). For a power of 90% and the hypothesis that vaginal deliveries will increase by 20%, (10% of patients lost to follow-up) 238 patients will need to be included in the study. The primary endpoint will be the rate of spontaneous vaginal deliveries (expected rate without rotation: 60%). The secondary endpoints will be the rate of fetal extractions (cesarean or instrumental) and the maternal and fetal morbidity and mortality rates. The intent-to-treat study will be conducted over 24 months. Recruitment started in February 2017. To achieve the primary objective, we will perform a test comparing the number of spontaneous vaginal deliveries in the two groups using Pearson's chi-squared test (provided that the conditions for using this test are satisfactory in terms of numbers). In the event that this test cannot be performed, we will use Fisher's exact test. Discussion: Given that the efficacy of manual rotation has not been proven with a high level of evidence, the practice of this technique is not systematically recommended by scholarly societies and is, therefore, rarely performed by obstetric gynecologists. If our hypothesis regarding the superiority of manual rotation is confirmed, our study will help change delivery practices in cases of posterior fetal position. An increase in the rates of vaginal delivery will help decrease the short-and long-term rates of morbidity and mortality following cesarean section. Manual rotation is a simple and effective method with a success rate of almost 90%. Several preliminary studies have shown that manual rotation is associated with reduced rates for fetal extraction and maternal complications: Shaffer has shown that the cesarean section rate is lower in patients for whom a manual rotation is performed successfully (2%) with a 9% rate of cesarean sections when manual rotation is performed versus 41% when it is not performed. Le Ray has shown that manual rotation significantly reduces vaginal delivery rates via fetal extraction (23.2% vs 38.7%, p < 0.01). However, manual rotation is not systematically performed due to the absence of proof of its efficacy in retrospective studies and quasi-experimental before/after studies.