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


  • Findings of this paper were presented at the 12th Annual Conference of the British Maternal and Fetal Medicine Society, Belfast, UK. 17,18 April 2007. Trial registration International Standard Randomised Controlled Trial Number Register, ISRCTN39772441.

Prof JE Norman, Chair of Maternal and Fetal Health, University of Edinburgh Centre for Reproductive Biology, The Queen’s Medical Research Institute, 47 Little France Crescent, Edinburgh. EH16 4TJ, UK. Email jane.norman@ed.ac.uk


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 ≥37 weeks gestation, requiring cervical ripening prior to induction of labour.

Methods  IMN (= 177) or placebo (= 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.