Impact of Attempted Mode of Delivery on Neonatal Outcomes in Nulliparous Individuals According to Body Mass Index

This study aimed to compare neonatal and maternal outcomes based on the attempted mode of delivery, stratified by prepregnancy body mass index (BMI; kg/m²) in nulliparous individuals.This was a repeated cross-sectional analysis of U.S. vital statistics Live Birth and Infant Death-linked data from 2011 to 2020. The analysis was restricted to nulliparas with singleton pregnancies and cephalic presentation who delivered at term. Our primary outcome was a composite neonatal outcome. We also examined a composite maternal outcome. We compared outcomes between individuals who attempted labor and those who opted for nonlabor cesarean delivery, categorized by BMI (<18.5, 18.5-24.9, 25-29.9, 30-39.9, ≥40). To account for significant differences in baseline characteristics between groups, Coarsened Exact Matching was applied using a k-to-k solution. We employed modified Poisson regression and calculated a difference-in-difference (DID) to compare differences in predicted proportions across BMI categories.Out of 9,709,958 individuals, 1,083,332 were included in the matched analysis. Compared with attempted vaginal delivery, nonlabor cesarean delivery was associated with an increased risk of the composite neonatal outcome across all BMI categories. However, the increase in risk was less pronounced in higher BMI categories compared with the reference group (BMI 18.5-24.9). For maternal outcomes, nonlabor cesarean delivery was associated with an increased risk of the composite maternal outcome in the BMI 18.5-24.9 and 25-29.9 categories. In contrast, the risk of adverse maternal outcomes associated with nonlabor cesarean delivery was lower in higher BMI groups compared with the reference group, with DID values ranging from -0.12 in the BMI 30-39.9 group to -0.16 in the BMI ≥40 group.Nonlabor cesarean delivery, as compared with attempted vaginal delivery, was associated with adverse neonatal outcomes across all BMI categories, though the relative increase in risk was diminished in higher BMI groups. · Compared with attempting vaginal delivery, nonlabor cesarean was associated with an increased risk of the composite neonatal outcome in all BMI classes (range of absolute risk difference 1.27-2.35%).. · The increased risk of the composite neonatal outcome was less pronounced in nulliparous individuals with a BMI of 40 kg/m2 or greater.. · Even for individuals with high BMI, attempting vaginal delivery is reasonable..