Abstract
OBJECTIVE: To quantify reporting errors, measure incidence of postpartum haemorrhage (PPH) and define risk factors for PPH (≥500 ml) and progression to severe PPH (≥1500 ml). DESIGN: Prospective observational study. SETTING: Two UK maternity services. POPULATION: Women giving birth between 1 August 2008 and 31 July 2009 (n = 10 213). METHODS: Weighted sampling with sequential adjustment by multivariate analysis. MAIN OUTCOME MEASURES: Incidence and risk factors for PPH and progression to severe PPH. RESULTS: Errors in transcribing blood volume were frequent (14%) with evidence of threshold preference and avoidance. The incidences of PPH ≥500, ≥1500 and ≥2500 ml were 33.7% (95% CI 31.2-36.2), 3.9% (95% CI 3.3-4.6) and 0.8% (95% CI 0.6-1.0). New independent risk factors predicting PPH ≥ 500 ml included Black African ethnicity (adjusted odds ratio [aOR] 1.77, 95% CI 1.31-2.39) and assisted conception (aOR 2.93, 95% CI 1.30-6.59). Modelling demonstrated how prepregnancy- and pregnancy-acquired factors may be mediated through intrapartum events, including caesarean section, elective (aOR 24.4, 95% CI 5.53-108.00) or emergency (aOR 40.5, 95% CI 16.30-101.00), and retained placenta (aOR 21.3, 95% CI 8.31-54.7). New risk factors were identified for progression to severe PPH, including index of multiple deprivation (education, skills and training) (aOR 1.75, 95% CI 1.11-2.74), multiparity without caesarean section (aOR 1.65, 95% CI 1.20-2.28) and administration of steroids for fetal reasons (aOR 2.00, 95% CI 1.24-3.22). CONCLUSIONS: Sequential, interacting, traditional and new risk factors explain the highest rates of PPH and severe PPH reported to date.