Objective To determine the safety and efficacy of intramuscular oxytocin plus ergometrine compared to intravenous oxytocin for prevention of postpartum haemorrhage, and the significance of administration at the end of the second stage of labour compared with that after the third stage.

Design A prospective cohort study.

Setting A university affiliated tertiary medical centre.

Participants Two thousand one hundred and eighty–nine women delivering singletons during 40 consecutive weeks.

Main outcome measures Postpartum haemorrhage (> 500 ml), prolonged third stage (> 30 min), retained placenta (>60min), elevated blood pressure (systolic > 150 mmHg, diastolic > 100 mmHg).

Results The rate of postpartum haemorrhage was not significantly different for oxytocinergometrine compared with oxytocin, when administered at the end of the second stage of labour (odds ratio 1.10, 95% confidence interval (CI) 0.75–1.61) or after the third stage (odds ratio 0.95, 95% CI 0.68–1.34). The patients receiving oxytocics at the end of the second stage of labour had significantly lower rates of postparturn haemorrhage, for both oxytocinergometrine (odds ratio 0.69, 95% CI 0.49–0.98) and oxytocin (odds ratio 0.60, 95% CI 0.41–0.87), compared with those treated after the third stage.

Conclusion Administration of oxytocin alone is as effective as the use of oxytocin plus ergometrine in the prevention of postpartum haemorrhage, but associated with a significantly lower rate of unpleasant maternal side effects. Oxytocics administered after delivery of the fetal head compared with after the placental expulsion are associated with a significantly lower rate of postpartum haemorrhage.