Randomized trial of isosorbide mononitrate versus misoprostol for cervical ripening at term

Abstract

Objectives: To assess the adverse effects of isosorbide mononitrate (IMN) compared with misoprostol for cervical ripening at term. Methods: One hundred and seven women with term pregnancies referred for induction of labor with Bishop scores of 6 or less were randomly allocated to receive either a 40-mg IMN tablet vaginally ( n=55) or 50 μg misoprostol vaginally ( n=52) every 6 h for a maximum of three doses. They were sent to the labor ward for amniotomy or oxytocin if either their Bishop scores were more than 6 or their cervices were not ripe 24 h after the treatment. Adverse effects, progress, and outcomes of labor were assessed. Results: Isosorbide mononitrate was associated with fewer adverse effects especially uterine tachysystole (0 vs. 19.2%, P<0.01) and hyperstimulation (0 vs. 15.4%, P<0.01). The time from start of medication to vaginal delivery in IMN group was significantly longer (25.6±6.1 vs. 14±6.9 h, P<0.01). Oxytocin was needed in 51 women (92%) of the isosorbide mononitrate group and six women (11%) of the misoprostol group ( P<0.001). The cesarean rate was not significantly different between the groups, but the major indications were different: dystocia (45%) in the IMN group vs. persistent non-reassuring fetal heart rate pattern (56%) in the misoprostol group. Conclusions: Cervical ripening with IMN resulted in fewer adverse effects, but was less effective than misoprostol.