Cervical ripening with mechanical method vs oral misoprostol in pregnancies with elevated BMI: a cohort study

To compare labour duration and the effectiveness of cervical ripening by transcervical balloon versus oral misoprostol in women with elevated body mass index (BMI ≥ 25 kg/m²).

A retrospective single-centre cohort (2022-2024) at Montpellier University Hospital including singleton term pregnancies (37-42 weeks) with cephalic presentation, BMI > 25 and Bishop score < 6. Mechanical balloon versus oral misoprostol (25 µg/2 h or 50 µg/4 h) were compared by survival analysis assessing induction-to-delivery interval and by logistic regression assessing vaginal delivery rates, all adjusting for key covariates.

maternal age < 18 years, scarred uterus, low-lying placenta.

Among 7336 births, 2225 (30.3%) underwent labour induction, of which 247 met inclusion criteria. Vaginal delivery occurred in 180/247 (72.9%), of which 21/180(11.7%) were operative vaginal, caesareans were 67/247(27.1%), with no statistically significant difference observed; the study was not powered to assess equivalence of caesarean rates. Balloons achieved shorter induction-to-delivery (Mean 25.5 h; 95%CI 23.8-27.2 h vs. 35.3 h; 95%CI 33.0-37.6 h; p < 0.001), and induction-to-active-phase intervals vs. misoprostol (Mean 21.1 h; SD 12.8 h vs. 30.3 h; SD 17.7 h; p < 0.001), without difference in first active-stage and second-stage duration or among misoprostol regimens. Cox regression identified predictors of longer induction-to-delivery: nulliparity (HR:0.31; 95%CI 0.22-0.42), misoprostol (HR:0.46; 95%CI 0.33-0.66) vs intrauterine balloons, LGA (HR:0.63; 95%CI 0.43-0.92), higher BMI (HR:0.97; 95%CI 0.97-1.00), and excessive weight gain (HR:0.98; 95%CI 0.95-1.00). Treatment-by-parity and treatment-by-Bishop score interactions were not significant. A Fine and Gray competing-risks model showed that mechanical ripening vs. misoprostol provided shorter time intervals from induction to delivery (p = 0.033) and to active phase (p = 0.003). After one cycle of ripening, oxytocin infusion was associated with a higher rate of vaginal birth compared with repeated ripening (sHR 2.28, 95%CI 1.49-3.49). PPH or adverse neonatal outcomes were not different.

In a high-BMI population mechanical cervical ripening vs. oral misoprostol show similar effectiveness, with the first associated with a shorter duration of labour induction.