Risks associated with prolonged latent phase of labor.

We sought to assess the impact of a prolonged latent phase (PLP) on maternal and neonatal morbidity.   This is a secondary analysis of a prospective cohort study conducted 2010-2015 that included all term gravidas who reached active labor (six centimeters). Primary outcomes were composite maternal morbidity (maternal fever, postpartum hemorrhage, transfusion, endometritis, and severe perineal lacerations) and composite neonatal morbidity (respiratory distress syndrome, mechanical ventilation, birth injury, seizures, hypoxic ischemic encephalopathy, therapeutic hypothermia, or umbilical artery pH < 7.1). Outcomes were compared between patients with and without PLP, defined as > 90th percentile of labor duration between admission and active phase. Results were stratified by induction (IOL) vs. spontaneous labor. A stratified analysis was performed by mode of delivery. Multivariable logistic regression was used to adjust for confounders. In this cohort of 6509 patients, 51% underwent induction of labor. 650 patients had a PLP with a median length of 8.5 hours in spontaneous labor and 18.8 hours in IOL. Among patients with PLP, there was a significant increase in composite maternal morbidity with both IOL (aOR 1.36, 95% CI 1.01, 1.84) and spontaneous labor (aOR 1.49, 95% CI 1.09, 2.04) and an increase in composite neonatal morbidity with spontaneous labor only (aOR 1.57, 95% CI 1.01, 2.45). Cesarean delivery occurred more often in PLP group (14.0% versus 25.1%). Among patients who underwent cesarean delivery, PLP remained associated with increased odds of maternal morbidity compared to those with normal latent phase. PLP at or above the 90th percentile in patients who reach active labor is associated with increased risk of maternal morbidity that is not mediated by cesarean delivery. PLP in spontaneous labor is associated with increased neonatal morbidity. These data suggest that further research is needed to establish latent phase cut-offs that may be incorporated into labor management guidelines.