Optimal misoprostol dosing among patients with a body mass index greater than 30: a randomized controlled trial

Patients with obesity experience an increased duration of labor with an increased risk for perinatal morbidity. When compared with parturients without obesity, they also experience fewer uterine contractions after administration of misoprostol. It is unclear if 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.

This study aimed to determine if 50 μg compared with 25 μg of vaginal misoprostol reduced the time from induction start to delivery among patients with obesity.

We performed a double-blinded, pragmatic randomized controlled trial, between June 1, 2022, and July 17, 2023. Patients with a body mass index ≥30 kg/m² who underwent labor induction at ≥ 36 weeks' gestation, had a singleton gestation, and a cervical dilation ≤3 cm at admission were included. Patients were excluded if they had a contraindication to vaginal delivery or misoprostol administration. Patients were randomized to 25 or 50 μg of vaginal misoprostol, stratified by parity, body mass index <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 that 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 by intention-to-treat. A 2-sample t test was used for the primary outcome, Cohen's d was used as a measure of effect, and P values were reported.

Of the 180 patients randomized, 88 were assigned to the 25 μg group and 92 were assigned to the 50 μg group. Of those, 96.1% of patients received the designated intervention. The 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=.28; 95% confidence interval, -0.02 to 0.57). In a planned subgroup analysis, multiparous patients delivered faster in the 50 μg group (15.2 hours vs 12.0 hours; d=.51; 95% confidence interval, 0.04-0.97). The risk for 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.

Patients with obesity who underwent cervical ripening with 50 μg of vaginal misoprostol experienced a similar time to delivery when compared with those who received 25 μg of misoprostol. However, multiparous patients had a significantly reduced time to delivery when 50 μg was used. A higher dose of misoprostol may be a promising intervention for reducing time in labor, which warrants further study.