Incidence and risk factors for severe postpartum haemorrhage in women with anterior low-lying or praevia placenta and prior caesarean: Prospective population-based study.

OBJECTIVE: To assess the incidence and risk factors for severe postpartum haemorrhage (PPH) in women with an anterior low-lying or praevia placenta, prior caesarean and no prenatal suspicion of placenta accreta spectrum (PAS). DESIGN: Population-based study in 176 maternity units in France. POPULATION: All women with anterior low-lying (0-19 mm from the cervical internal os) or praevia placenta, diagnosed prospectively before birth, prior caesarean and no prenatal suspicion of PAS. METHODS: Multivariable logistic regression to identify risk factors for severe PPH in the main population and after exclusion of women with PAS diagnosed only at birth. MAIN OUTCOME MEASURES: Severe PPH defined by a composite criterion either estimated blood loss of ≥1500 ml, transfusion of ≥4 or more units of packed red blood cells, embolisation or surgical treatment. RESULTS: Of the 520 114 women constituting the source population, 230 (0.44/1000 women; 95% confidence interval [CI] 0.38-0.50) met the inclusion criteria. Severe PPH rate was 24.8% (95% CI 19.2-30.4) overall, 27.5% (95% CI 21.8-33.3) in women with placenta praevia and 15.4% (95% CI 10.7-20.0) in women with low-lying placenta. PAS was diagnosed at birth in 22 women (9.9%; 95% CI 5.8-13.4), although previously unsuspected. After their exclusion, severe PPH incidence was 17.3% (95% CI 12.4-22.2). In multivariate analysis, the only factor associated with a higher severe PPH risk was placenta previa (aOR, 3.65; 95%CI, 1.20-15.8). CONCLUSION: Severe PPH is frequent among women with anterior low-lying or praevia placenta and prior caesarean, even after exclusion of women with PAS. The risk of severe PPH for those with praevia is nearly twice that with low-lying placenta.