The association between the length of first stage of labor, mode of delivery, and perinatal outcomes in women undergoing induction of labor

Objective: To estimate the association between the lengths of the first stage of labor, mode of delivery, and perinatal outcomes in women undergoing labor induction. Study Design: Retrospective cohort study of singleton, term pregnancies with labor induction and delivered during the second stage. The length of the first stage was examined by 6-hour intervals as predictors of mode of delivery and perinatal morbidity using χ² test and multivariable logistic regression analysis. Results: There were 3620 women who met study criteria. Compared with women with a first stage between 0-12 hours, women with longer first stages had a higher risk of cesarean delivery during the second stage, up to an adjusted odds ratio of 7.44 in those with a first stage ≥24 hours (95% confidence interval [CI], 3.43-16.1). Women with a first stage ≥24 hours also had higher odds of postpartum hemorrhage (adjusted odds ratio [aOR], 3.16; 95% CI, 1.73-5.79), chorioamnionitis (aOR, 2.83; 95% CI, 1.19-6.69), and neonatal admission to the intensive care nursery (aOR, 2.03; 95% CI, 1.10-3.74). Conclusion: In women who underwent induction of labor, even when a second stage of labor was reached, the risk for cesarean delivery and maternal morbidity remained increased when the length of the first stage was longer than 24 hours. However, in this clinical scenario, the frequency of cesarean delivery remains less than 50%. The decision for surgical intervention thus should not be based on the elapse of time alone.