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Maternal Obesity on Postpartum Hemorrhage: Effect Modification by Mode of Delivery.
Abstract Number: SAT-17
Abstract Type: Original Research
Introduction: Obesity has been associated with postpartum hemorrhage (PPH) risk. Also, the risk of PPH varies according to mode of delivery. However, it is unclear whether the relations between maternal BMI and PPH vary according to mode of delivery.
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 the California OSPHD Data Center. PPH cases were identified using ICD-9 codes (666.x). For the main exposure of interest, pre-pregnancy body mass index (BMI) was categorized using the WHO criteria for adult underweight, overweight, and obesity class 1, 2, and 3. We utilized mixed effects logistic regression models stratified by mode of delivery to analyze the risk of PPH according to BMI class, accounting for relevant maternal and obstetric confounders. Secondary analyses were performed for 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 prevalences in each BMI group stratified by mode of delivery (spontaneous vaginal delivery [SVD]; instrumental delivery [ID], and cesarean delivery [CD]) are presented in Table 1. Table 1 presents our stratified data analyses. Among SVDs, compared to those with normal BMI, the adjusted odds of PPH were increased for overweight women (aOR=1.09; 95% CI=1.07-1.12), obesity class I women (aOR=1.17; 95% CI=1.13-1.2), obesity class II women (aOR=1.12; 95% CI=1.06-1.17), and obesity class III women (aOR= 1.15; 95% CI=1.08-1.23). Among IDs, overweight and obese women were not at increased odds of PPH or atonic PPH. Among CDs, the risk of PPH decreased with increases degrees of obesity. Similar findings were observed with models examining atonic PPH. No evidence of interaction was observed between maternal obesity and delivery mode in a logistic model with severe PPH as the outcome of interest.
Conclusion: After SVD, obese women are at slightly increased risk of PPH and atonic PPH. In contrast, after CD, obesity was protective against PPH. The strength and magnitude of the associations were similar between BMI class with PPH and atonic PPH after stratifying for mode of delivery. These findings suggest a modifying effect of delivery mode on the association between obesity and PPH, which warrants further investigation.