Nitric oxide donor isosorbide mononitrate for pre-induction cervical ripening at 41 weeks' gestation: A randomized controlled trial

Abstract

Objective: Nitric oxide donors have been shown to cause cervical ripening. The aim of this study was to determine whether sustained release isosorbide mononitrate (ISMN-SR) 60 mg administered vaginally is effective for pre induction cervical ripening at 41 weeks' gestation.

Methods: A double-blind randomised controlled trial was carried out at the University Obstetric Unit, Galle, Sri Lanka for a period of 9 months, commencing 1st August 2003. One hundred and fifty-six consecutive women with uncomplicated singleton pregnancies at 41 weeks' gestation with a modified Bishop Score <5 were allocated by stratified (primip/multip) block randomization to receive either ISMN-SR 60 mg (n = 78) or vitamin C 100 mg (n = 78) vaginally. Modified Bishop Score at 41 weeks + 2 days' gestation and the proportions establishing spontaneous labor or becoming favorable for induction of labor (IOL) by 41 weeks + 2 days' gestation were evaluated in each group.

Results: At the commencement of the study there were no differences between the mean age, parity or modified Bishop Score of the two groups. In the ISMN-SR group, there was a marked increase in the proportion establishing spontaneous labor (28% vs 7.5%, P < 0.01) and being favorable for IOL (40% vs 9% P < 0.001), 2 days after therapy. In the ISMN-SR group, there was a significantly higher increase in the mean modified Bishop Score (3.8, 95% CI 2.3-5.3 vs 1.3, 95% CI 0.3-2.2, P < 0.01) and a marked decrease in the proportion of subjects requiring further ripening of the cervix with a Foley catheter. (32% vs 79%, P < 0.001). The cesarean section rates were similar in both groups.

Conclusion: Sustained release ISMN administered vaginally is effective for preinduction cervical ripening.