Increased length of active labor is associated with adverse perinatal outcomes among nulliparous women undergoing labor induction

Evaluate the association between current recommendations for active labor duration in nulliparous women undergoing labor induction and adverse perinatal outcomes.Retrospective cohort study from 2012 to 2015. Subjects were nulliparous, 18-44 years, cephalic, singleton ≥37 weeks undergoing labor induction who reached active labor. We created three subgroups, defined by active labor duration from 6 to 10cm as the median, median-95th percentile, and95th percentile based on contemporary labor curves. We evaluated the association between subgroups and cesarean delivery, chorioamnionitis, blood loss (EBL), 5-minute Apgar score7, and neonatal intensive care unit (NICU) admission using logistic regression.Among 356 women, 34.8% had an active labor duration median, 43.3% were between the median-95th percentile, and 21.9% were95th percentile. The risk of cesarean delivery increased with longer active labor duration; 1.8-fold (95%CI = 1.1-3.1) and 4.0-fold (95%CI = 2.5-6.5) for women whose active labors were between the median-95th percentile and95th percentile, respectively. Chorioamnionitis increased by 3.9-fold (95%CI = 1.2-13.2) in the95th percentile subgroup. Active labor length was not associated with EBL, Apgar scores, or NICU admission.Cesarean delivery and chorioamnionitis increased significantly as induced active labor duration exceeded the median. This study provides a better understanding regarding the risks of longer active labor as defined by contemporary labor curves.