Objective: To assess risk factors for postpartum hemorrhage (PPH) and the extent to which changes in those risk factors may explain the rising incidence of PPH recently reported from industrialized countries.
Methods: We carried out a hospital-based cohort study of 103 726 consecutive deliveries from January 1, 1978, to January 31, 2007, from the computerized medical records of a tertiary-care university maternity hospital in Montreal. We examined adjusted odds ratios for any PPH (estimated blood loss > 500 mL for vaginal deliveries, > 1000 mL for Caesarean sections), severe PPH (estimated blood loss ≥ 1500 mL), and PPH accompanied by blood transfusion and/or hysterectomy.
Results: Major independent risk factors for PPH included primiparity, prior Caesarean section, placenta previa or low-lying placenta, marginal umbilical cord insertion in the placenta, transverse lie, labour induction and augmentation, uterine or cervical trauma at delivery, gestational age < 32 weeks, and birth weight ≥ 4500 g. An overall increase in rate of PPH over the study period (OR 1.029; 95% CI 1.024 to 1.034 per year) disappeared (OR 0.995; 95% CI 0.988 to 1.001 per year) after inclusion of maternal age, parity, prior Caesarean section, labour induction and augmentation, placenta previa or low-lying placenta, and abnormal placenta, with most of the reduction attributable to rises in previous Caesarean section and labour augmentation.
Conclusion: Labour induction, augmentation of labour, and prior Caesarean section are significantly associated with the risk of PPH, and their increase over the study period largely explains the observed rise in PPH.