Mediating processes underlying the associations between maternal obesity and the likelihood of cesarean birth.

Background: Pregnant women with obesity are more likely to experience cesarean birth compared to women without obesity. Yet, little is known about the underlying mechanisms. The objective of this study was therefore to evaluate how mediators contribute to the association between obesity and prelabor/intrapartum cesarean birth.

Methods: We retrospectively analyzed Swiss cohort data from 394,812 singleton, cephalic deliveries between 2005 and 2020. Obesity (BMI ≥ 30 kg/m ) was defined as the exposure and prelabor or intrapartum cesarean birth as the outcomes. Hypothesized mediators included gestational comorbidities, large-for-gestational-age infant, pregnancy duration >41 weeks, slower labor progress, labor induction, and history of cesarean birth. We performed path analyses using generalized structural equation modeling and assessed mediation by a counterfactual approach.

Results: Women with obesity had a cesarean birth rate of 39.36% vs. 24.12% in women without obesity. The path models mainly showed positive direct and indirect associations between obesity and cesarean birth. In the total sample, the mediation models explained up to 39.47% (95% CI 36.92-42.02) of the association between obesity and cesarean birth, and up to 57.13% (95% CI 54.10-60.16) when including history of cesarean birth as mediator in multiparous women. Slower labor progress and history of cesarean birth were found to be the most clinically significant mediators.

Conclusions: This study provides empirical insights into how obesity may increase cesarean birth rates through mediating processes. Particularly allowing for a slower labor progress in women with obesity might reduce cesarean birth rates and prevent subsequent repeat cesarean births in multiparous women.