• Azar Mehrabadi, Jennifer A Hutcheon, Shiliang Liu, Sharon Bartholomew, Michael S Kramer, Robert M Liston, K S Joseph, and Maternal Health Study Group of Canadian Perinatal Surveillance System (Public Health Agency of Canada).
• Department of Obstetrics and Gynaecology, University of British Columbia and the Children's and Women's Hospital & Health Centre of British Columbia, and the School of Population and Public Health, University of British Columbia, Vancouver, British Columbia, the Maternal and Infant Health Section, Public Health Agency of Canada, Ottawa, Ontario, and the Departments of Pediatrics and Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Quebec, Canada.
• Obstet Gynecol. 2015 Apr 1;125(4):814-21.

ObjectiveTo quantify the contribution of placenta accreta to the rate of postpartum hemorrhage and severe postpartum hemorrhage.MethodsAll hospital deliveries in Canada (excluding Quebec) for the years 2009 and 2010 (N=570,637) were included in a retrospective cohort study using data from the Canadian Institute for Health Information. Placenta accreta included placental adhesion to the uterine wall, musculature, and surrounding organs (accreta, increta, or percreta). Severe postpartum hemorrhage included postpartum hemorrhage with blood transfusion, hysterectomy, or other procedures to control bleeding (including uterine suturing and ligation or embolization of pelvic arteries). Rates, rate ratios, population-attributable fractions (ie, incidence of postpartum hemorrhage attributable to placenta accreta), and 95% confidence intervals (CIs) were estimated. Logistic regression was used to quantify associations between placenta accreta and risk factors.ResultsThe incidence of placenta accreta was 14.4 (95% CI 13.4-15.4) per 10,000 deliveries (819 cases among 570,637 deliveries), whereas the incidence of placenta accreta with postpartum hemorrhage was 7.2 (95% CI 6.5-8.0) per 10,000 deliveries. Postpartum hemorrhage among women with placenta accreta was predominantly third-stage hemorrhage (41% of all cases). Although placenta accreta was strongly associated with postpartum hemorrhage (rate ratio 8.3, 95% CI 7.7-8.9), its low frequency resulted in a small population-attributable fraction (1.0%, 95% CI 0.93-1.16). However, the strong association between placenta accreta and postpartum hemorrhage with hysterectomy (rate ratio 286, 95% CI 226-361) resulted in a population-attributable fraction of 29.0% (95% CI 24.3-34.3).ConclusionPlacenta accreta is too infrequent to account for the recent temporal increase in postpartum hemorrhage but contributes substantially to the proportion of postpartum hemorrhage with hysterectomy.

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