The impact of body mass index on misoprostol dosing for labor induction: a comparison of vaginal and buccal dosage forms.

Abstract

Despite the increasing prevalence of obesity, strategies to manage induction of labor in obese patients remains underinvestigated. This study aimed to determine whether the number of doses to achieve active labor differed across body mass index categories for buccal misoprostol vs vaginal misoprostol during labor induction. This was a secondary analysis of the Induction with MisoPROsotol: Oral mucosa versus Vaginal Epithelium study (identification number: NCT02408315), a triple-blinded, placebo-controlled randomized controlled trial of vaginal misoprostol vs buccal misoprostol in term patients undergoing labor induction. The primary outcome for this analysis was the number of doses of misoprostol needed for active labor (defined as a cervical dilation of at least 6 cm). The participants were grouped into 3 body mass index categories (nonobese: ≤29 kg/m²; obese: 30-40 kg/m²; morbidly obese: ≥41 kg/m²). Groups were compared using the Wilcoxon signed-rank test and chi-squared or Fisher exact test. Generalized linear models were used to adjust for ethnicity, race, dosing route, and indication for labor induction. Significance was defined as P<.05. Of 299 participants with complete data, 63 (21%) had a body mass index of ≤29 kg/m², 165 (55%) had a body mass index between 30 and 40 kg/m², and 71 (23%) had a body mass index of ≥41 kg/m². The groups did not differ in age, race, gestational age, nulliparity, initial Bishop score, or route of dosing. There were significantly more non-Hispanic participants in the obese categories (P=.02). A higher proportion of participants with obesity or morbid obesity had diabetes mellitus (6.4% in the nonobese group vs 13.9% in the obese group vs 14.1% in the morbidly obese group) or a hypertensive disorder (7.9% in the nonobese group vs 24.9% in the obese group vs 26.8% in the morbidly obese group) as the primary indication for labor induction (P=.03). In the univariate analysis, compared with the nonobese group, more doses of misoprostol were needed to achieve active labor in the obese and morbidly obese groups when dosed buccally (2.1 vs 2.8 vs 2.9, respectively; P=.01) but not when dosed vaginally (1.9 vs 2.1 vs 2.3, respectively; P=.21). The rates of vaginal delivery in <24 hours, cesarean delivery, or cesarean delivery for fetal distress did not significantly differ across body mass index category or dosing route. When adjusting for indication for labor induction and self-reported race/ethnicity, buccal dosing required more doses to achieve active labor, regardless of body mass index (24% more expected doses; P<.005). Similarly, when controlling for indication for labor induction and self-reported race/ethnicity, obesity was independently associated with requiring more doses for active labor for both dosage routes (body mass index of 30-40 kg/m²: 24% more expected doses; confidence limits of 1.01-2.68; P<.047; body mass index of ≥41 kg/m²: 28% more expected doses; confidence limits of 0.99-3.09; P<.05). Obesity (body mass index of ≥30 kg/m²) was associated with the need for more misoprostol doses to achieve active labor. In addition, buccal dosing was independently associated with a higher number of doses than vaginal dosing, especially in patients with obesity.