BackgroundMost guidelines propose inducing labor within 24 h following term (37 or more weeks of gestation) prelabor rupture of membranes (PROM). However, the exact timing for initiating induction within the 24 h period remains unknown. This study aims to comparatively assess the efficacy and safety of the use of vaginal dinoprostone within 6 h versus within 6–24 h for singleton pregnancies with PROM and an unfavorable cervix (Bishop score < 6).MethodsThis was a retrospective cohort study including singleton pregnancies with PROM and an unfavorable cervix (Bishop score < 6) in which labor was induced using vaginal dinoprostone. Women were divided into two groups according to the timing of the use of induction (within 6 h versus within 6–24 h after PROM). Baseline maternal data, maternal and neonatal outcomes were recorded for statistical analysis.Results450 women were included, 146 (32.4%) of whom were induced within 6 h of PROM and 304 (67.6%) were induced within 6–24 h. Cesarean delivery rate (15.8% versus 29.3%, p = 0.002) and nonreassuring fetal heart rate tracing (4.8% versus 10.5%, p = 0.043) in group with vaginal dinoprostone within 6 h were significantly lower than those in group with vaginal dinoprostone within 6–24 h. There was no significant differences in terms of duration from IOL to vaginal delivery.ConclusionInduction of labor within 6 h with vaginal dinoprostone after PROM for singleton pregnancies with an unfavorable cervix (Bishop score < 6) significantly associated with less cesarean section, less nonreassuring fetal heart rate tracing, compared to induction of labor within 6–24 h after PROM.