Predicting postpartum hemorrhage in women undergoing planned cesarean section: A multicenter retrospective cohort study in Japan.

Given Japan's unique social background, it is critical to understand the current risk factors for postpartum hemorrhage (PPH) to effectively manage the condition, especially among specific groups. Therefore, this study aimed to identify the current risk factors for PPH during planned cesarean section (CS) in Japan. This multicenter retrospective cohort study was conducted in two tertiary maternal-fetal medicine units in Fukushima, Japan and included 1,069 women who underwent planned CS between January 1, 2013, and December 31, 2022. Risk factors for PPH (of > 1000 g and > 1500 g) were assessed using multivariate logistic regression analysis, considering variables such as maternal age, parity, assisted reproductive technology (ART) pregnancy, pre-pregnancy body mass index (BMI), uterine myoma, placenta previa, gestational age at delivery, birth weight categories, and hypertensive disorders of pregnancy (HDP). Multivariate linear regression analyses were conducted to predict estimated blood loss during planned CS. ART pregnancy, a pre-pregnancy BMI of 25.0-29.9 kg/m2, and uterine myoma increased PPH risk at various levels. Maternal smoking increased the risk of >1500 g PPH (adjusted odds ratio: 3.09, 95% confidence interval [CI]: 1.16-8.20). Multivariate linear analysis showed that advanced maternal age (B: 83 g; 95% CI: 27-139 g), ART pregnancy (B: 239 g; 95% CI: 121-357 g), pre-pregnancy BMI of 25.0-29.9 kg/m2 (B: 74 g; 95% CI: 22-167 g), uterine myoma (B: 151 g; 95% CI: 47-256 g), smoking (B: 107 g; 95% CI: 13-200 g), and birth weight > 3,500 g (B: 203 g; 95% CI: 67-338 g) were associated with blood loss during planned CS. Considering a patient's clinical characteristic may help predict bleeding in planned CSs and help improve patient safety.