Defining the upper limit of the second stage of labor in nulliparous patients

Background: Increased duration of the second stage of labor provides clinical challenges in decision-making regarding the optimal mode of delivery that minimizes maternal and neonatal morbidity.

Objective: In a large cohort of uncomplicated nulliparous singleton cephalic labors, we sought to examine the effect of increasing duration of second stage on delivery and perinatal outcome.

Study design: The GENESIS Study recruited 2336 nulliparous patients with vertex presentation in a prospective double-blinded study to examine prenatal and intrapartum predictors of delivery. Metrics included maternal demographics, duration of second stage, mode of delivery, and associated maternal and neonatal outcomes. Indicators of morbidity included third- or fourth-degree tear, postpartum hemorrhage, neonatal intensive care unit admission, low Apgar scores, cord pH <7.20 and a composite of birth injury that included cephalohematoma, fetal laceration, brachial plexus palsy, facial nerve palsy, and fetal fracture.

Results: Of 2336 recruited nulliparous participants, 1872 reached the second stage of labor and had complete data for analysis. Increased maternal age (P=.02) and birthweight (P<.001) were found to be associated with a longer second stage. Increasing second stage duration was found to impact on mode of delivery, such that at <1 hour duration the spontaneous vaginal delivery rate was 63% vs 24% at >3 hours (P<.001). Operative vaginal delivery increased from 35% at <1 hour to 65% at >3 hours (P<.001). The rate of cesarean delivery increased with duration of the second stage from 1.2% at <1 hour to 11% at >3 hours (P<.001). The rates of third- or fourth-degree tear increased with second stage duration (P=.003), as did postpartum hemorrhage (P<.001). The composite neonatal birth injury rate increased from 1.8% at <1 hour to 3.4% at >3 hours. The maximum rate of birth injury was 6.5% at 2-3 hours (P<.001). Multiple logistic regression analysis that controlled for maternal age and birthweight confirmed that operative vaginal delivery, perineal trauma, postpartum hemorrhage, and neonatal birth injury remained significantly more likely with increasing second stage duration.

Conclusion: In a prospective cohort of nulliparous pregnancies, increasing duration of second stage of labor was associated with increased rates of operative vaginal and cesarean delivery. Although almost 90% of term nulliparous women with a second stage of labor >3 hours will succeed in achieving a vaginal birth, this success comes at a maternal morbidity cost, with a 10% risk of severe perineal injury and an increasing rate of significant neonatal injury.