The cost-effectiveness of outpatient (at home) cervical ripening with isosorbide mononitrate prior to induction of labour

Objectives  To assess the cost-effectiveness of outpatient (at home) cervical ripening with isosorbide mononitrate (IMN) prior to induction of labour. Design  Economic evaluation was conducted alongside a randomised placebo controlled trial (the IMOP trial). Setting  Large UK maternity hospital. Population  A total of 350 nulliparous women with a singleton pregnancy, cephalic presentation ≥37 weeks gestation, requiring cervical ripening prior to induction of labour. Interventions  Isosorbide mononitrate (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. Results  Mean health service costs between the period of randomisation and discharge for mother and infant were £1254.86 in the IMN group and £1242.88 in the placebo group, generating a mean cost difference of £11.98 (bootstrap mean cost difference £12.86; 95%CI: −£106.79, £129.39) that was not statistically significant (P = 0.842). The incremental cost per hour prevented from hospital admission to delivery was £7.53. At the notional willingness to pay threshold of £100 per hour prevented from hospital admission to delivery, the probability that IMN is cost-effective was estimated at 0.67. This translated into a mean net monetary benefit of £98.13 for each woman given IMN. Conclusions  Although the probability that IMN is cost-effective approaches 0.7 at seemingly low willingness to pay thresholds for an hour prevented from hospital admission to delivery, our results should be viewed in the light of the clinical findings from the IMOP trial.