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 > or = 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 pound sterling in the IMN group and 1242.88 pound sterling in the placebo group, generating a mean cost difference of 11.98 pound sterling (bootstrap mean cost difference 12.86 pound sterling; 95%CI: -106.79 pound sterling, 129.39 pound sterling) that was not statistically significant (P = 0.842). The incremental cost per hour prevented from hospital admission to delivery was 7.53 pound sterling. At the notional willingness to pay threshold of 100 pound sterling 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 pound sterling 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.