The impact of isosorbide mononitrate on cervical ripening and labor induction in primiparous women with term pregnancy: A double-blind, randomized, controlled trial

BACKGROUND: The most favorable method for cervical ripening is not fully agreed upon by practitioners; however, vaginal administration of isosorbide mononitrate (IMN) is considered a low-risk method of labor induction for pregnant women at full term. Our study was designed to assess the effect of IMN on cervical ripening and labor induction among primiparous women in Iran. MATERIALS AND METHODS: A randomized, double-blind, placebo-controlled trial was conducted on 90 primiparous women with Bishop score ≤ 5, term pregnancy, and no sign of labor. The women were allocated into two groups to receive either a 40 mg (2 × 20 mg) IMN tablet vaginally (n = 45) or placebo (n = 45) at 0 and 12 h. If uterine contractions were not present after 24 h, women were sent to the labor section for induction of labor. Bishop score, reason for induction, duration of active, second, and third phase of labor, and mode of delivery were assessed. RESULTS: There was a significant difference between the IMN group and the controls with respect to the Bishop score (4.92 vs. 4.03, P = 0.0.01), induction to active phase interval (387.6 vs. 520.4 min, P = 0.03), the length of induction (350 vs. 446 min, P = 0.03), and the drug administration to delivery interval (33.9 vs. 36.2 h, P = 0.03). The major side effect of IMN was headache, which responded to analgesia. CONCLUSIONS: IMN can be an effective alternative drug for cervical ripening and could decrease the labor interval. Further studies are necessary to fully address the benefits of IMN, especially in pregnancies of gestational age greater than 42 weeks.