Design: Secondary analysis of the vaginal misoprostol arm of a cluster randomised trial
Population: 1,322 women ≥37 weeks with cervix ≤2 cm; 264 with BMI ≥40
Primary outcome: Induction-to-delivery time and mode of delivery
Effect: Adjusted mean difference +3.5 h (95% CI 1.9–4.8); vaginal birth aOR 0.6 (0.4–0.8)

This secondary analysis took the vaginal misoprostol arm of a cluster randomised trial of vaginal versus oral misoprostol at term. All 1,322 women had a cervix dilated 2 cm or less and followed the same protocol: 25 µg every three hours for up to five doses, then standardised oxytocin. One in five (264) had a BMI of 40 or more at delivery.

Women with severe obesity were more likely to start with a closed cervix. After adjustment for clustering, starting dilatation, hypertension and diabetes, their inductions lasted about 3.5 hours longer overall (95% CI 1.9 to 4.8), with a longer first stage and longer oxytocin use. They needed more misoprostol doses and had lower odds of vaginal birth (adjusted OR 0.6, 0.4 to 0.8).

This is useful for counselling and planning rather than for changing the regimen. The authors raise alternative protocols for this group, but the analysis did not test one.

Counsel women with BMI 40 or more that induction with vaginal misoprostol is likely to take several hours longer.
Plan labour ward staffing and bed time for longer inductions in this group.
Expect more misoprostol doses and a longer oxytocin phase before declaring induction failed.
Discuss the lower chance of vaginal birth honestly at the induction decision.
Do not change the misoprostol regimen on this analysis alone; no alternative protocol was tested.

Why it matters

A longer induction is expected in this group, which changes when a slow induction should be called a failed one.

The statistics, in plain English

An adjusted odds ratio of 0.6 means the odds of vaginal birth were about 40% lower with severe obesity, after accounting for the factors listed. The interval (0.4 to 0.8) excludes 1. Because this compares groups within one trial arm rather than randomising by BMI, it describes how these women labour; it does not say what would help.