10 Optimal Misoprostol Dosing Among Patients with a BMI Greater Than 30: A Randomized Controlled Trial

BACKGROUND:Patients with obesity experience an increased duration of labor with increased risk of perinatal morbidity. Compared to parturients without obesity, they also experience fewer uterine contractions after administration of misoprostol. It is unclear whether the same dose of misoprostol should be used for induction of labor in patients with obesity compared to non-obese patients. Therefore, we sought to investigate if a higher dose of misoprostol for patients with obesity is more effective. OBJECTIVE:To determine if 50mcg compared to 25mcg of vaginal misoprostol reduces the time from induction start to delivery in patients with obesity. STUDY DESIGN:We performed a double-blinded, pragmatic randomized controlled trial, between June 1, 2022, and July 17, 2023. Patients with a body mass index (BMI) ≥ 30 kg/m2 undergoing labor induction ≥ 36 weeks, singleton gestations, and a cervical dilation ≤ 3cm on admission, were included. Patients were excluded if they had a contraindication to vaginal delivery or misoprostol administration. Patients were randomized to 25 or 50 mcg of vaginal misoprostol, stratified by parity, BMI < 40 kg/m2 or ≥ 40 kg/m2, and provider intent to use mechanical dilation at the onset of labor induction. Usual labor management was followed at the discretion of the provider. The primary outcome was time from induction to delivery. A priori, we estimated 90 subjects per group (N=180) were needed for an 85% power to detect a 3-hour difference between groups with a type I error of 5%. Analysis was intention-to-treat. A two-sample t-test was used for the primary outcome, Cohen's d as a measure of effect, and P values were reported. RESULTS:Of the 180 patients randomized, 88 were assigned to the 25mcg group and 92 were assigned to the 50mcg group. 96.1% of patients received the designated intervention. Baseline characteristics were similar between groups. No difference was found in the primary outcome of time to delivery (21.6 hours vs. 18.6 hours; d = 0.28; 95% confidence interval, -0.02-0.57). In a planned subgroup analysis, multiparous patients delivered faster in the 50mcg group (15.2 hours vs. 12.0 hours; d = 0.51; 95% confidence interval, 0.04-0.97). The risk of tachysystole associated with fetal heart tracing changes was rare overall (2.2%) and not significantly different between groups. No differences in maternal or neonatal adverse effects were observed. CONCLUSION:Patients with obesity undergoing cervical ripening with 50mcg of vaginal misoprostol experienced similar time to delivery when compared to 25mcg. However, multiparous patients had a significantly reduced time to delivery when 50mcg was used. A higher dose of misoprostol may be a promising intervention for reducing time in labor which warrants further study.