Design: Secondary analysis of the vaginal misoprostol arm of a cluster randomised trial
Population: 1,322 term inductions, 264 with BMI 40 or more
Primary outcome: Induction duration and mode of delivery
Effect: Total duration +3.5 h (1.9 to 4.8); vaginal delivery aOR 0.6 (0.4 to 0.8)

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

After adjustment for clustering, starting dilatation, hypertension and diabetes, women with severe obesity had a total induction about 3.5 hours longer (95% CI 1.9 to 4.8), a first stage 2.2 hours longer (0.6 to 3.8) and 2.5 hours more oxytocin (1.1 to 3.8). They needed more misoprostol doses and had lower odds of vaginal delivery (aOR 0.6, 0.4 to 0.8).

None of this changes the decision to induce. It does change the conversation before induction and the planning of ward time. Women with severe obesity benefit from hearing a realistic estimate of duration, and units can expect these inductions to occupy a bed longer. Whether a different regimen would do better was not tested here.

Tell women with a BMI of 40 or more that induction with vaginal misoprostol is likely to take several hours longer.
Expect more misoprostol doses and longer oxytocin use when planning delivery-suite capacity.
Record BMI at the time of induction, not only at booking, because the analysis used BMI at delivery.
Discuss the lower chance of vaginal birth honestly during consent for induction.
Do not switch to an untested regimen on this evidence; the study compared groups, not protocols.

Why it matters

A longer induction is predictable, so it should be part of consent rather than a surprise on the ward.

The statistics, in plain English

An adjusted odds ratio of 0.6 means about 40% lower odds of vaginal birth; the interval 0.4 to 0.8 stays below 1.0. This is a comparison within one trial arm, so it describes what happens with this regimen in heavier women rather than testing anything new.