Randomised placebo-controlled trial of outpatient (at home) cervical ripening with isosorbide mononitrate (IMN) prior to induction of labour--clinical trial with analyses of efficacy and acceptability. The IMOP study

Abstract

Objective: To determine whether isosorbide mononitrate (IMN), self-administered vaginally by women at home, improves the process of induction of labour.

Design: Randomised double blind placebo-controlled trial.

Setting: Large UK maternity hospital.

Population or sample: Nulliparous women with a singleton pregnancy, cephalic presentation > or = 37 weeks gestation, requiring cervical ripening prior to induction of labour.

Methods: IMN (n = 177) or placebo (n = 173) self-administered vaginally at home at 48, 32 and 16 hours prior to the scheduled time of admission for induction.

Main outcome measures: Admission to delivery interval and women's experience of induction of labour.

Results: IMN did not shorten the admission to delivery interval as compared with placebo [mean difference of -1.6 hours (95% CI -5.1,1.9, P = 0.37)], despite being more effective than placebo in inducing a change in Bishop score [mean difference of 0.65 (95% CI 0.14,1.17, P = 0.013)]. While both groups found the overall experience of home treatment to be positive, (mean score of 3.8/10 +/- 2.3/10 for the IMN group, where 1 = extremely good and 10 = not at all good) women in the placebo group found it marginally more positive than those in the IMN group (just over half a unit on a 10-point scale, P = 0.043). There were no differences between the groups in the pain or anxiety experienced or willingness to take the treatment in a subsequent pregnancy.

Conclusions: IMN self-administered vaginally at home does not shorten admission to delivery interval despite a significant effect on cervical ripeness assessed using the Bishop score. However, women report positive views on cervical ripening at home, and the setting deserves further investigation.