32: Second stage of labor outcomes in nulliparous patients with prolonged first stage of labor

Abstract

Contemporary labor curves suggest that a wide variation in first stage duration may be normal. We tested the hypothesis that a prolonged first stage of labor in nulliparas who reach complete cervical dilation is associated with a lower likelihood of spontaneous vaginal delivery (SVD). Planned secondary analysis from the Optimizing Management of the Second Stage (OMSS) multicenter randomized trial in which nulliparas with term pregnancies and neuraxial analgesia were assigned at complete dilation to immediate or delayed pushing. The primary outcome was SVD. Secondary outcomes were operative vaginal delivery, cesarean, 3rd/4th degree lacerations, postpartum hemorrhage, 2nd stage chorioamnionitis, duration of 2nd stage and pushing, shoulder dystocia, and composite neonatal morbidity defined as occurrence of one or more of: death, birth injury, acidemia, respiratory distress, transient tachypnea, meconium aspiration with pulmonary hypertension, hypoxic-ischemic encephalopathy, hypoglycemia, hypothermia treatment, or suspected neonatal sepsis. Multivariable logistic regression was used to estimate aOR for outcomes with prolonged first stage of labor, defined as first stage duration >90th percentile of the cohort. First stage duration was determined by the interval between admission and completion dilation. Of the 2404 patients in the trial, 2349 had data on first stage duration and were included in this analysis. The 90th percentile for first stage duration was 12.7 hours. Rates of immediate and delayed pushing were similar between groups. Patients with a prolonged first stage were less likely to have a SVD compared to those without a prolonged first stage (aOR 0.65, 95% CI 0.46, 0.94). Patients with a prolonged first stage were at higher risk for cesarean (aOR 2.14, 95%CI 1.40, 3.26) and chorioamnionitis (aOR 1.86, 95% CI 1.22, 2.84). Other secondary outcomes were similar between groups. A prolonged first stage of labor in nulliparous women is associated with a lower likelihood of SVD even when patients reach complete cervical dilation.