Exploring the effects of obesity on postpartum hemorrhage risk

Objective This study aims to analyze rates of postpartum hemorrhage according to body mass index (BMI) and to investigate relative risks for postpartum hemorrhage based on body mass index. Study Design We conducted a retrospective chart review of all deliveries occurring in 2022 at two large urban hospitals in Indianapolis, Indiana, resulting in a cohort of 5686 patients. After excluding patients for missing data, a total of 4493 patients were included in the final analysis. Patients were categorized according to the CDC BMI definitions. We analyzed rates of postpartum hemorrhage according to patient variables. Results The rates of postpartum hemorrhage for patients with BMI categorized as healthy weight, overweight, Class 1 obesity, Class 2 obesity, and Class 3 obesity were 16.3%, 19.6%, 23.0%, 21.3%, and 27.7%, respectively (p<0.0001). Relative risk for postpartum hemorrhage by BMI categories was investigated using logistic regression analysis, where patients in the healthy weight cohort (BMI 18- <25) were used as the reference for risk of postpartum hemorrhage. We found that patients with Class 3 obesity had an increased risk of postpartum hemorrhage by 57% after adjusting for mode of delivery and race (aRR 1.57, 95% CI 1.20-2.04). Despite increased relative risk in all categories, we found no statistical significance for patients with BMI in the overweight category (aRR 1.19, 95% CI 0.92-1.54) or the Class 2 obesity category (aRR 1.24, 95% CI 0.05-1.63). Conclusion This study shows a significantly increased risk of postpartum hemorrhage among obese patients, particularly those with class 3 obesity. Notably, we did not observe a dose-dependent effect of BMI on rates of postpartum hemorrhage as there was in fact a marginal decrease in rates of postpartum hemorrhage when comparing Class 1 and Class 2 obesity. This study supports risk-based initiatives to address increasing postpartum hemorrhage rates in the United States.