Randomized trial of two doses of the prostaglandin E1 analog misoprostol for labor induction

Our purpose was to compare the safety and effectiveness of intravaginally administered misoprostol at doses of 25 micrograms and 50 micrograms for indicated labor induction in patients with an unfavorable cervix.

Three hundred ninety-nine patients received either 25 micrograms or 50 micrograms of misoprostol, placed intravaginally in the posterior fornix, in this randomized double-blind trial. The dose was repeated every 3 hours until adequate labor was achieved (at least three contractions in 10 minutes).

Among 399 patients evaluated, 192 patients were allocated to the 25 micrograms group and 207 patients to the 50 micrograms group. The start-to-delivery interval was shorter in the 50 micrograms group (826 minutes vs 970 minutes, p = 0.02). The incidence of vaginal delivery after one dose was higher in the 50 micrograms group (38.2% vs 25.0%, p = 0.007). Patients receiving 25 micrograms required oxytocin augmentation more frequently than did those receiving 50 micrograms (27.1% vs 16.9%, p = 0.02). No differences were noted in the cesarean or other operative delivery rates among patients in the two treatment groups. The incidence of newborns with a cord pH < 7.16 was greater in the 50 micrograms group (13.0% vs 6.8%, p = 0.04). Although the incidence of hyperstimulation was similar between the groups, the incidence of tachysystole was higher in the 50 micrograms group (32.8% vs 15.6%, p = 0.0001).

Although a dose of 50 micrograms is associated with a shorter start-to-delivery interval and a higher incidence of vaginal delivery after one dose, 25 micrograms of intravaginal misoprostol is effective and associated with a lower incidence of tachysystole and cord pH values < 7.16.