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

Abstract

ObjectiveTo determine risk factors for cesarean delivery in nulliparas at labor admission.Study DesignNulliparas with liveborn, 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.ResultOf 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 <1cm, 1-3cm, 4cm, and ≥5cm dilated respectively. The BMI influence was most evident in the <1cm dilation category with 26% of BMI<25 and 66% of BMI≥40 having a cesarean delivery. The fewest cesarean deliveries (5%) occurred in those ≥5cm and BMI<25. In the multivariate regression analysis, first cervical dilation exam <1cm (OR 5.1, 95%CI 4.5-5.7; reference ≥5cm) and BMI≥40 (OR 5.1, 95%CI 4.6-5.7; reference BMI<25.0) had the highest odds for cesarean delivery.ConclusionCervical dilation on admission followed by BMI were the two most important risk factors for cesarean delivery identified in both CART and multivariate regression analysis.