Ten percent of pregnancies beyond 36 weeks' gestation are complicated by spontaneous premature rupture of membranes. Multiple studies have compared the use of expectant management with the use of active labor induction in women who do not begin spontaneous labor following membrane rupture. Traditionally, labor is induced to prevent chorioamnionitis and neonatal sepsis. The use of intravenous oxytocin and the incidence of cesarean delivery are lower when prostaglandins are applied to ripen the cervix. Misoprostol, a synthetic prostaglandin E1 analog, has been shown to be as effective in inducing labor as dinoprostone. Wing and Paul prospectively compared vaginally administered misoprostol with intravenous oxytocin for labor induction in women with ruptured membranes who have not begun labor.
A total of 197 women were randomized to treatment: 98 women received misoprostol and 99 received oxytocin. A 25-μg dose of misoprostol was placed in the posterior vaginal fornix. If adequate uterine contraction frequency was not demonstrated, a single repeat dose of misoprostol was administered six hours later. Oxytocin was given intravenously by an incremental infusion protocol to a maximum of 20 mU per minute.
The mean estimated gestational age of the patients in both groups was 38 weeks. A similar percentage of subjects in both treatment groups had a treatment success. A total of 76 percent of the misoprostol-treated group and 74 percent of the oxytocin-treated group delivered vaginally within 24 hours of treatment initiation. Parity influenced the success of labor induction, regardless of the treatment arm. In the misoprostol group, 63 percent of nulliparous women and 86 percent of multiparous women were delivered within 24 hours. In the oxytocin group, 60 percent of the nulliparous patients and 86 percent of the multiparous group were delivered in the same time period. The duration from induction to delivery in both groups was similar. Thirty of the women who were treated with misoprostol required two doses. Uterine hyperstimulation did not occur in either treatment group. Abnormal fetal heart rate monitor tracings occurred equally in both groups.
Evidence of intra-amniotic infection was equal in both groups (about 27 percent). Neonatal sepsis was suspected in 21 percent of infants born to misoprostol-treated women and in 27 percent of infants born to oxytocin-treated women. Approximately 86 percent of women receiving misoprostol were delivered vaginally, compared with 83 percent of women treated with oxytocin. In the misoprostol-treated group, 13 women had cesarean deliveries; in the oxytocin-treated group, 17 women had cesarean deliveries. Neonatal outcomes did not differ between treatment groups.
The authors conclude that vaginal administration of misoprostol is an effective alternative to oxytocin infusion for labor induction. Because the majority of cesarean deliveries in the misoprostol-treated women were performed for labor dystocia rather than for failed induction, misoprostol appears to be effective in causing cervical dilatation and effacement, and in inducing labor when premature rupture of the membranes has occurred.