Objective: To estimate whether maternal obesity was associated with an increased risk for postpartum hemorrhage more than 1,000 mL and whether there was an association between maternal obesity and causes of postpartum hemorrhage and mode of delivery.
Methods: A population-based cohort study including 1,114,071 women with singleton pregnancies who gave birth in Sweden from January 1, 1997 through December 31, 2008, who were divided into six body mass index (BMI) classes. Obese women (class I-III) were compared with normal-weight women concerning the risk for postpartum hemorrhage after suitable adjustments. The use of heparin-like drugs over the BMI strata was analyzed in a subgroup.
Results: There was an increased prevalence of postpartum hemorrhage over the study period associated primarily with changes in maternal characteristics. The risk of atonic uterine hemorrhage increased rapidly with increasing BMI. There was a twofold increased risk in obesity class III (1.8%). No association was found between postpartum hemorrhage with retained placenta and maternal obesity. There was an increased risk for postpartum hemorrhage for women with a BMI of 40 or higher (5.2%) after normal delivery (odds ratio [OR] 1.23, 95% confidence interval [CI] 1.04-1.45]) compared with normal-weight women (4.4%) and even more pronounced (13.6%) after instrumental delivery (OR 1.69, 95% CI 1.22-2.34) compared with normal-weight women (8.8%). Maternal obesity was a risk factor for the use of heparin-like drugs (OR 2.86, 95% CI 2.22-3.68).
Conclusion: The increased risk for atonic postpartum hemorrhage in the obese group has important clinical implications, such as considering administration of prophylactic postpartum uterotonic drugs to this group.
Level of evidence: II.