When has an induction failed?

OBJECTIVE: To evaluate the length of the latent phase that, during labor inductions in nulliparous women, is associated with significantly decreased chance of vaginal delivery and increased risk of maternal and neonatal morbidity.
METHODS: All inductions of labor during a 6-month period were identified. Only those women who were nulliparous with a pregnancy of 36 weeks or more of gestation underwent further data analysis. Demographic data, intrapartum course, and maternal and neonatal outcomes were abstracted from the medical record. The latent phase was defined as beginning after oxytocin had been initiated and amniotomy performed and continuing until either 4 cm cervical dilation and 80% effacement or 5 cm cervical dilation regardless of effacement.
RESULTS: A total of 397 nulliparous women, 32% of whom underwent cervical ripening, presented during the study period. Only 8 women (2%) never achieved active phase labor before cesarean, and the overall cesarean rate was 26.0%. A longer latent phase was associated with a greater rate of cesarean delivery, although only after 18 hours did a majority of induced labors result in cesarean. Chorioamnionitis and postpartum hemorrhage were more frequent with latent phases of labor greater than 18 hours (16% and 26%, respectively), although these diagnoses did not translate into greater risk of transfusion, hysterectomy, or prolonged hospitalization. Neonatal outcomes, including meconium passage, fetal acidemia, neonatal intensive care unit admission, or other morbidity did not increase in conjunction with longer latent phases.
CONCLUSION: A latent phase of as long as 18 hours during induction of labor in nulliparous women allows the majority of these women to achieve a vaginal delivery without being subject to a significantly increased risk of significant maternal or neonatal morbidity. LEVEL OF EVIDENCE: II-2.