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. LEVEL OF EVIDENCE II.