Objective: Our purpose was to compare two dosing regimens of vaginally administered misoprostol for preinduction cervical ripening and induction of labor.
Study design: Five hundred twenty-two patients with indications for induction of labor and unfavorable cervices were randomly assigned to one of two dosing regimens of vaginally administered misoprostol. Twenty-five microgram tablets of misoprostol were placed in the posterior vaginal fornix either every 3 hours to a maximum of eight doses or every 6 hours to a maximum of four doses. The maximal period of cervical ripening was 24 hours regardless of the number of misoprostol doses administered. Medication was not given after either spontaneous rupture of membranes or the beginning of active labor.
Results: Among 522 patients enrolled, 261 were randomized to receive misoprostol every 3 hours and 261 to receive misoprostol every 6 hours. The average interval from start of induction to vaginal delivery was shorter in the 3-hour dosing group (1311.74 +/- 785.14 minutes) than in the 6-hour dosing group (1476.96 +/- 805.30 minutes) (p < 0.05). Oxytocin augmentation of labor occurred more commonly in the 6-hour dosing group (51.4%) than in the 3-hour dosing group (41.8%) (p < 0.05) [corrected]. There were no significant differences between routes of delivery. Overall, 108 patients (20.8%) were delivered by cesarean section. There was a slightly higher prevalence of tachysystole (six or more uterine contractions in a 10-minute window for two consecutive 10-minute periods) in the 3-hour group (14.6%) than in the 6-hour group (11.2%), but this difference was not statistically different. There were no significant differences in the frequency of uterine hyperstimulation or hypertonus. There was no significant difference between groups in the frequency of abnormal fetal heart rate tracings, meconium passage, 1- or 5-minute Apgar scores < 7, neonatal resuscitations, or admissions to the neonatal intensive care unit.
Conclusions: Vaginally administered misoprostol is an effective agent for cervical ripening and induction of labor. Patients with the 6-hour dosing schedule had longer intervals to delivery, more frequently required oxytocin augmentation, and had more failed inductions than did patients with 3-hour dosing. Further investigation to characterize the safety of misoprostol is needed.