Postpartum haemorrhage in nulliparous women: incidence and risk factors in low and high risk women. A Dutch population-based cohort study on standard (> or = 500 ml) and severe (> or = 1000 ml) postpartum haemorrhage.

Objective: To determine the incidence and risk factors for standard and severe postpartum haemorrhage (PPH) in vaginally delivering nulliparous women, before and after risk stratification.

Study Design: A population-based cohort study in an unselected cohort nulliparous women (N = 3464) in 'The Zaanstreek' district, The Netherlands. Risk stratification is part of routine care, where midwives cover all obstetrical care for women with low risk pregnancies.

Results: The incidence of standard PPH (> or = 500 ml) and severe PPH (> or = 1000 ml) were 19 and 4.2%, respectively. A retained placenta occurred in 1.8%. These data show consistently slightly higher values as compared to studies in literature. The most important risk factors for standard and severe PPH were related to an abnormal third stage of labour-third stage > or = 30 min and retained placenta (in severe PPH: odds ratio (OR) 14.1, 95% confidence interval (CI) 10.4-19.1). High birth weight and perineal damage were less important, but independent, significant risk factors. In the low risk group (N = 1416), incidence of severe PPH was 4.0%. Independent risk factors for severe PPH were third stage > or = 30 min (incidence 7.1%, OR 3.6) and retained placenta (incidence 1.2%, OR 21.6). In 25% of the women with a prolonged third stage (> or = 30 min), third stage was complicated due to retained placenta and/or severe PPH (1.8% of the low risk group).

Conclusions: The incidence of PPH in nulliparous women in this cohort was on average higher than published data, while the most important risk factors for standard and severe PPH, even after risk stratification, were the same. A prolonged third stage of labour has to be considered as abnormal, requiring specific action.