Objective: To compare maternal and neonatal outcomes based on length of the latent phase during induction with rupture of membranes before 6 cm dilation.
Methods: This is a retrospective cohort study using data from the Consortium of Safe Labor study, including 9,763 nulliparous and 8,379 multiparous women with singleton, term pregnancies undergoing induction at 2 cm dilation or less with rupture of membranes before 6 cm dilation after which the latent phase ended. Outcomes were evaluated according to duration of oxytocin and rupture of membranes.
Results: At time points from 6 to 18 hours of oxytocin and rupture of membranes, the rates of nulliparous women remaining in the latent phase declined (35.9-1.4%) and the rates of vaginal delivery for those remaining in the latent phase at these time periods decreased (54.1-29.9%) Nulliparous women remaining in the latent phase for 12 hours compared with women who had exited the latent phase had significantly increased rates of chorioamnionitis (12.1% compared with 4.1%) and endometritis (3.6% compared with 1.3%) and increased rates of neonatal intensive care unit admission (8.7% compared with 6.3%). Similar patterns were present for multiparous women at 15 hours.
Conclusion: Based on when neonatal morbidity increased, in an otherwise uncomplicated induction of labor with rupture of membranes, a latent phase after initiation of oxytocin of at least 12 hours for nulliparous women and 15 hours in multiparous women is a reasonable criterion for diagnosing a failed induction.