Objective  To compare the effectiveness of immediate induction of labour with vaginal misoprostol versus expectant management for 24 hours followed by oxytocin induction in women with premature rupture of membranes at term (term PROM).

Design  An open, randomised, controlled trial.

Setting  Public university hospital in Campinas City, Brazil.

Population  One hundred and fifty pregnancies, half of them allocated to each group.

Methods  Statistical analysis used Student's t test, the χ2 test, Fisher's exact test, survival analysis and risk ratio estimates with 95% CI.

Main outcome measures  Latency period, recruitment to delivery period, period of hospitalisation, mode of delivery, contractility pattern, fetal wellbeing, labour and delivery complications, neonatal and maternal morbidity.

Results  Both groups had similar general characteristics, but the misoprostol group had a significantly shorter latency period (9.4 vs 15.8 hours), a shorter time interval from recruitment to delivery (18.9 vs 27.5 hours), a shorter period of maternal hospitalisation and a slightly higher proportion of alterations of contractility when compared with the expectant group. Caesarean section rates were 20% in the misoprostol group and 30.7% in the other. There were no differences between them regarding fetal wellbeing, complications during labour and delivery and neonatal or postpartum maternal morbidity. Within 24 hours, 44% of women had delivered in the expectant group against 73.3% in the misoprostol group.

Conclusions  Immediate labour induction with misoprostol in cases of term PROM shortens the latency period, the total time between recruitment to delivery and the time of maternal hospitalisation, increasing the occurrence of alterations of contractility without any maternal and perinatal outcomes disadvantages.