Risks Associated with Prolonged Latent Phase of Labor.

Objective:  We sought to assess the impact of a prolonged latent phase (PLP) on maternal and neonatal morbidity.

Study design:  This is a secondary analysis of a prospective cohort study conducted 2010 to 2015 that included all term gravidas who reached active labor (6 cm). 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 of labor (IOL) versus spontaneous labor. A stratified analysis was performed by mode of delivery. Multivariable logistic regression was used to adjust for confounders.

Results:  In this cohort of 6,509 patients, 51% underwent IOL. A total of 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 (adjusted odds ratio [aOR]: 1.36, 95% confidence interval [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 vs. 25.1%). Among patients who underwent cesarean delivery, PLP remained associated with increased odds of maternal morbidity compared with those with normal latent phase.

Conclusion:  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 cutoffs that may be incorporated into labor management guidelines.

Key points: · Latent labor ≥90th percentile is associated with increased maternal morbidity in induced and spontaneous labor.. · Latent labor ≥90th percentile in spontaneous but not induced labor is associated with increased neonatal morbidity.. · Cesarean delivery alone does not explain this increased maternal morbidity..