Intrapartum cesarean delivery in nulliparas: risk factors compared by two analytical approaches

Objective:to determine risk factors for cesarean delivery in nulliparas at labor admission.study design:nulliparas with live-born, singleton gestations ⩾37 weeks in spontaneous or induced labor were analyzed from the consortium on safe labor database in a retrospective observational study. classification and regression tree (cart) and multivariate logistic regression analysis determined risk factors for cesarean delivery.result:of the 66 539 nulliparas, 22% had a cesarean delivery. in the cart analysis, the first cervical dilation exam was the first branch followed by body mass index (bmi). cesarean deliveries occurred in 45%, 25%, 14% and 10% of deliveries at <1 , 1 to 3, 4 and ⩾5 cm dilated, respectively. the bmi influence was most evident in the <1 cm dilation category with 26% of bmi <25 kg m−2 and 66% of bmi ⩾40 kg m−2 having a cesarean delivery. the fewest cesarean deliveries (5%) occurred in those ⩾5 cm and bmi <25 kg m−2. in the multivariate regression analysis, first cervical dilation exam <1 cm (odds ratio (or) 5.1, 95% confidence interval (ci): 4.5 to 5.7; reference ⩾5 cm) and bmi ⩾40 kg m−2 (or 5.1, 95% ci: 4.6 to 5.7; reference bmi <25.0 kg m−2) had the highest odds for cesarean delivery.conclusion:cervical dilation on admission followed by bmi were the two most important risk factors for cesarean delivery identified in both cart and multivariate regression analysis.