Objective  To test the safety and efficacy of prostaglandin E2 (PgE2) as a treatment for dystocia in spontaneous labour.

Design  Randomised, double-blind, placebo-controlled trial.

Setting  Multicentre study in nine university-affiliated hospitals in Canada.

Population  Three hundred and thiry-two nulliparous women with spontaneous labour at term.

Methods  Women who had progressed <2 cm of cervical dilation in the 4 hours following the diagnosis of labour were randomly assigned to receive a single dose of either 1 mg (n= 112) or 2 mg (n= 111) PgE2 vaginal gel or placebo gel (n= 109).

Main outcome measures  The primary outcome was resolution of dystocia, defined as a change in cervical dilatation of >0.5 cm per hour in the 6 hours following gel administration. Secondary outcomes were progress of labour, uterine hyperstimulation (more than five contractions in 10 minutes or a contraction lasting more than 2 minutes), use of oxytocin, method of delivery, maternal and neonatal morbidity.

Results  Dystocia resolved more often after PgE2 1 mg (49%), RR 1.53 (95% CI 1.1, 2.1) and PgE2 2 mg (49%), RR 1.5 (CI 1.1, 2.1), compared with placebo (32%). Hyperstimulation was increased after PgE2 2 mg treatment (15%), RR 5.6 (95% CI 1.7, 18), but not after PgE2 1 mg (5.4%), RR 1.9 (CI 0.50, 7.6) when compared with placebo (2.8%). There was an increase in caesarean sections performed in the second stage of labour in the PgE2 groups versus placebo. There were no differences in measures of maternal or neonatal morbidity.

Conclusion  A single 1-mg dose of PgE2 vaginal gel is more effective than placebo in resolving dystocia, without increasing uterine hyperstimulation, but may be associated with an increase in the incidence of second stage caesarean section.