Length of the first stage of labor and associated perinatal outcomes in nulliparous women

Objective: To estimate whether length of the first stage of labor is associated with adverse maternal and neonatal outcomes. Methods: This is a retrospective cohort study of nulliparous women with term, singleton gestations delivered in one academic center between 1990 and 2008. The length of the first stage was stratified into three subgroups: less than the 5th percentile, 5th to 95th percentile, and greater than the 95th percentile. Maternal and neonatal outcomes were compared using the χ test. Multivariable logistic regression models were used to control for confounders. Results: Of the 10,661 nulliparous women meeting study criteria, the median (50th percentile) length of the first stage was 10.5 hours. Compared with women with a first stage between 2.8 and 30 hours (5th to 95th percentile thresholds), the risk of cesarean delivery was higher (6.1% compared with 13.5%; adjusted odds ratio [OR], 2.28, 95% confidence interval [CI], 1.92-2.72) in women with a first stage longer than 30 hours (greater than the 95th percentile). These women also had higher odds of chorioamnionitis (12.5% compared with 23.5%; adjusted OR, 1.58; 95% CI, 1.25-1.98) and neonatal admission to the neonatal intensive care unit (4.7% compared with 9.8%; adjusted OR, 1.53; 95% CI, 1.18-1.97) but no other associated adverse neonatal outcomes. Conclusion: Women with a prolonged first stage of labor have higher odds of cesarean delivery and chorioamnionitis, but their neonates are not at risk of increased morbidity.