Osmotic dilators vs. Foley balloons: Bayesian secondary analyses of the DILAFOL trial

Dilapan-S, a synthetic osmotic dilator used for pre-induction cervical ripening, has proven to be as effective as the Foley balloon in terms of vaginal versus cesarean delivery and has been associated with increased patient satisfaction. Nevertheless, its ability to lower cesarean rates and its cost-effectiveness remain poorly studied.

To estimate the likelihood that synthetic osmotic dilators reduce cesarean deliveries and to evaluate their health system costs (2026 US$) and incremental cost-effectiveness compared to the Foley balloon during cervical ripening.

Secondary Bayesian analyses were conducted using data from the single-center DILAFOL randomized controlled trial, which enrolled 419 parturients at ≥37 weeks' gestation with singleton pregnancies undergoing labor induction with an unfavorable cervix. Participants were randomized to receive synthetic osmotic dilators (n = 208) or a Foley balloon (n = 209) for cervical ripening. A Bayesian logistic regression model was used to estimate the probability of a reduced cesarean delivery rate with synthetic osmotic dilators. Health system costs were evaluated using Bayesian generalized linear models. The incremental cost-effectiveness ratio (ICER) was derived from these models using neutral priors, assuming no treatment effect.

In intent-to-treat analysis, synthetic osmotic dilators had an 89% probability of reducing cesarean delivery compared to the Foley balloon (mean absolute risk difference, -5.0% (95% credible interval [CrI], [-12.8 to 2.7). Mean total obstetric cost per patient was $10,198 for synthetic osmotic dilators and $10,176 for Foley (RR, 1.00; 95% CrI, 0.94 - 1.06). Although synthetic osmotic dilators cost $399 per patient, this was largely offset by an 85% probability of reduced hospital costs ($8,771 vs. $9,081; RR, 0.97; 95% CrI, 0.90-1.03) and 99% probability of reduced physician costs ($1,028 vs. $1,094; RR, 0.94; 95% CrI, 0.89-0.99). The ICER of synthetic osmotic dilators versus Foley was $439 per cesarean delivery prevented (95% CrI, -$51,813 to $57, 697]), with 42% of posterior draws falling in the dominant quadrant (cost-saving and more effective). The probability of cost-effectiveness rose from 47% at $0 willingness-to-pay threshold to 85% at $15,000 per cesarean delivery prevented. Subgroup analyses suggested that economic benefits were most favorable among patients aged <35 years and nulliparous parturients, in whom the posterior probability of dominance was 52% and 39%, respectively.

Despite its higher material cost, synthetic osmotic dilators likely reduced cesarean delivery rates with minimal impact on total health system costs and a favorable cost-effectiveness profile. These findings, which do not account for neonatal costs or future pregnancy outcomes, suggest that osmotic dilators represent good value in obstetric care, particularly among younger and nulliparous patients. Further validation across obstetric settings is warranted.