Abstract Objective To assess the risk of severe postpartum haemorrhage (PPH) according to the durations of the passive and active phases of the second stage of labour. Study design Secondary analysis from the PREMODA prospective observational study in 138 French maternity units; 3330 low-risk nulliparous women with vaginal deliveries of cephalic singletons were included. Prospective analysis of the recorded durations of the active first stage of labour and the passive and active phases of the second stage of labour was undertaken, and their association with severe PPH, defined by estimated blood loss >1000 ml or blood transfusion. Factors associated with severe PPH were analysed by uni and multivariate analyses with logistic regression models. Results The frequency of severe PPH was 2.1% ( n = 69). In the univariate analysis, the frequency of severe PPH increased with the duration of the active second stage but not the passive second stage: 1.2% for active second stage <10 min, 1.6% for 10–19 min, 2.1% for 20–29 min, 2.6% for 30–39 min, 4.5% for 40–49 min and 14.3% for ≥50 min ( p < 0.001). After adjustment for confounding factors, the risk of severe PPH was found to be statistically significant when the active first stage exceeded 6 h [adjusted odds ratio (OR) 2.5, 95% confidence interval (CI) 1.0–6.1)] and when the active second stage exceeded 40 min (40–49 min: adjusted OR 3.5, 95% CI 1.0–12.3; ≥50 min: adjusted OR 10.6, 95% CI 2.8–40.3; reference: <10 min). The duration of the active second stage was not associated with other maternal or neonatal complications. Conclusions A prolonged active, but not passive, second stage of labour is associated with the risk of severe PPH in nulliparas. The optimal duration of these phases remains to be defined.