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Maternal Obesity and The Risk of Postpartum Hemorrhage: A Cohort Study.
Abstract Number: BP-03
Abstract Type: Original Research
Introduction: Postpartum hemorrhage (PPH) is the leading cause of maternal death globally. Identifying risk factors for PPH, such as maternal obesity, may improve risk-stratification, preparation, and resource allocation. Prior studies investigating the association between maternal obesity and PPH report inconsistent findings. Our aim was to examine the strength and direction of the association between maternal body mass index (BMI) with PPH in a large, population-based cohort, carefully attending to potential confounders in our study design.
Methods: We performed a retrospective, cohort study of women who delivered in California between 2008-2012. Linked patient discharge and birth certificate data were obtained from California OSPHD Data Center. PPH cases were identified using ICD-9 codes (666.x). For the main exposure of interest, pre-pregnancy BMI was categorized using the WHO criteria for adult underweight, overweight, and obesity class 1,2, and 3. We performed multilevel logistic regression to examine the association between BMI class with PPH, accounting for relevant maternal and obstetric confounders, with a random intercept for maternity units. Secondary analyses were performed, using ICD-9 codes, with atonic PPH and severe PPH (classified as PPH with transfusion) as outcome measures.
Results: There were 2,176,673 deliveries in our study cohort; PPH occurred in 60,704 (2.8%) of all deliveries. Rates of PPH according to BMI class were: underweight (2.4%), normal BMI (2.8%), overweight (2.9%), obese class I (2.8%), class II (2.6%), and class III (2.6%); P for trend=0.68. In the multilevel analysis, compared to women with a normal BMI, the adjusted odds of PPH were modestly increased for overweight women (aOR=1.06; 95% CI=1.04-1.08) and class 1 obese women (aOR=1.08; 95% CI=1.05-1.11) (Table). Of note, underweight women had a 8% reduced odds of PPH compared to those with normal BMI. Similar findings were observed in the model with atonic PPH (Table). In contrast, the odds of severe PPH was reduced for overweight women, and women with class 1, 2, and 3 obesity (Table).
Conclusion: Our findings demonstrate a small positive effect of maternal obesity on the risk of PPH and a stronger protective association between obesity and severe PPH. Because our analysis accounted for a broad set of confounders, residual confounding may explain why findings from prior studies were inconsistent.