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 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. 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 <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. 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.