775 Optimizing Latent Phase Duration During Inductions to Minimize Morbidity and Cesarean Delivery

A prolonged latent phase (PLP) is associated with maternal/neonatal morbidity. Although ACOG recommends against cesarean for PLP, the rising rate of patients undergoing induction of labor (IOL) demands identification of meaningful latent phase timepoints that can guide counseling/management. We aim to define the optimal latent phase length during IOL using maternal, neonatal, and cesarean risks. This was a secondary analysis of the Consortium for Safe Labor study, a multicenter retrospective study of consecutive births at 19 hospitals from 2002-2008. We included singleton, cephalic gestations at ≥ 37 weeks who underwent IOL and completed the latent phase. Pregnancies with prior uterine incisions, major congenital anomalies, and incomplete labor curve information were excluded. Composite maternal and neonatal morbidities (see figure) and likelihood of vaginal delivery (VD) were analyzed at each four-hour interval of latent phase past 12 hours. Results were stratified by parity. Multivariable logistic regression was used to determine adjusted odds ratios for cumulative risk. 13,161 patients were included with 6128 (47%) nulliparas and 7033(53%) multiparas. The composite maternal and neonatal morbidities were seen in 13% and 8% of patients, respectively. Among nulliparas undergoing IOL, cumulative risks of maternal and neonatal morbidity consistently increased after 16 and 20 hours, respectively. Although the odds of a VD decreased consistently with each time extension past 12 hours, the absolute chance of VD remained high at 74% even at >24 hours of latent phase for nulliparas. Among multiparas undergoing IOL, the odds of neonatal morbidity increased at 12 hours but then remained stable, whereas maternal morbidity did not increase with time. The odds of VD decreased at each time point after 12 hours, but VD rates remained >78% at >24 hours for multiparas. In nulliparous patients undergoing IOL, 20 hours of latent labor is a reasonable timepoint to engage in shared decision-making about increased risks of maternal and neonatal morbidity and chances of VD.