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Am Fam Physician. 1999;59(3):675-680

Misoprostol, a synthetic prostaglandin E1 analog, can initiate uterine contractions and has been reported to effectively induce labor. Some studies have found that vaginally administered misoprostol resulted in a shorter time to delivery than orally administered misoprostol but was associated with tachysystole and hyperstimulation of the uterus, which theoretically could lead to increased risk of operative delivery and neonatal asphyxia. Bennett and colleagues compared the effectiveness and incidence of adverse effects of misoprostol administered orally with misoprostol given vaginally in the induction of labor in women who were of at least 37 weeks' gestation.

Data were compared from 206 Canadian women who met the criteria for safe induction of labor for anticipated vaginal delivery. After screening and giving informed consent, patients were randomly assigned to receive misoprostol either orally or vaginally. To ensure the double-blind nature of the study, each patient received either active oral misoprostol (50 mg) plus vaginal placebo or active vaginal misoprostol (50 mg) plus oral placebo every four hours until the occurrence of one of the following: at least three contractions every 10 minutes, spontaneous rupture of the membranes or delivery, or a concern about fetal heart rate or other complications. The management of labor and delivery was determined by attending physicians, and each patient was monitored throughout the process. Patient satisfaction was assessed by questionnaire following delivery.

The mean time to delivery was significantly reduced in the 102 women treated vaginally (846 minutes) compared with the 104 treated orally (1,072 minutes). The two groups did not differ in analgesia, epidural anesthetic or oxytocin use. The two groups also had similar patterns of delivery with no difference in the rate of cesarean section or assisted delivery. Vaginal misoprostol was associated with increased rates of tachysystole and hyperstimulation, but the differences did not reach statistical significance. Neonatal outcomes were similar in both groups. The median Apgar scores at one and five minutes were identical in the two groups; however, more infants in the group whose mothers received vaginal misoprostol had an Apgar score of less than seven at one minute. Patient-reported data also showed no difference in the incidence of gastrointestinal upset or in general satisfaction.

The authors conclude that both oral and vaginally administered of misoprostol are safe and effective for induction of labor. Vaginal administration is associated with more rapid delivery, greater uterine activity and more frequent fetal heart rate graph abnormalities. This finding may reflect uncertainties about the optimal dosage of vaginal misoprostol. Until the optimal dosing interval for vaginal use is determined, the preferred route of misoprostol administration might be oral.

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