Misoprostol for induction of labour: a systematic review

Objective To determine, from the best available evidence, the effectiveness and safety of misoprostol administered vaginally or orally for third trime ster cervical ripening or induction of labour. Methods Clinical trials of misoprostol used for cervical ripening or labour induction in the third trimester were identified from the register of rand omised trials maintained by the Cochrane Pregnancy and Childbirth Group. Al l identified trials were considered for inclusion in the review according t o a prespecified protocol. Primary outcomes were chosen to address clinical effectiveness (delivery within 24 hours) and safety (uterine hyperstimulat ion, caesarean section, serious maternal and neonatal morbidity) and were d etermined a priori. All meta-analyses were based on the intention-to-treat principle. In the absence of heterogeneity the summary statistics have been expressed as typical relative risk (RR) and 95% confidence interval (CI). Results Vaginal misoprostol: one small study showed that the use of misopro stol results in more effective cervical ripening and reduced need for oxyto cin when compared with placebo. When compared with oxytocin, vaginal misopr ostol was more effective for labour induction. The relative risk of failure to achieve vaginal delivery within 24 hours was 0.48 (95% CI 0.35 to 0.66) . However, the relative risks for uterine hyperstimulation with and without fetal heart rate abnormalities were 2.54 (95% CI 1.12 to 5.77) and 2.96 (9 5% CI 2.11 to 4.14), respectively. In three out of four trials which studie d women with intact membranes and unfavourable cervices, failure to achieve vaginal delivery within 24 hours was reduced with misoprostol when compare d with ether prostaglandins (RR 0.71, 95% CI 0.62 to 0.81). Vaginal misopro stol was associated with increased uterine hyperstimulation both without fe tal heart rate changes (RR 1.67, 95% CI 1.30 to 2.14) and with associated f etal heart rate changes (RR 1.45, 95% CI 1.04 to 2.04). There was also an i ncrease in meconium stained amniotic fluid following vaginal misoprostol (R R 1.38, 95% CI 1.06 to 1.79). Oral misoprostol: one small trial suggests th at, when compared with placebo, oral misoprostol reduces the need for oxyto cin and shortens the time between induction and delivery. Compared with oth er prostaglandins one small trial showed a reduced need for oxytocin with o ral misoprostol. Two trials compared oral with vaginal misoprostol using di fferent doses. No significant differences were evident. Conclusions Overall, misoprostol appears to be more effective than conventi onal methods of cervical ripening and labour induction. Although no differe nces in perinatal outcome were shown, the studies were not sufficiently lar ge to exclude the possibility of uncommon serious adverse effects. In parti cular the increase in uterine hyperstimulation with fetal heart rate change s following misoprostol is a matter for concern. It is possible that, if su fficient numbers are studied, an unacceptably high number of serious advers e events including uterine rupture and asphyxial fetal deaths may occur. Th e data at present are not robust enough to address the issue of safety. Thu s, though misoprostol shows promise as a highly effective, inexpensive and convenient agent for labour induction, it cannot be recommended for routine use at this stage. Lower dose misoprostol regimens should be investigated further.