Associations between body mass index and retained placenta in delivery hospitalizations: Analysis of the Nationwide Inpatient Sample, 2016–2020

Abstract Objective Retained placenta (RP) is an obstetric complication associated with postpartum hemorrhage, sepsis, and maternal morbidity. While maternal body mass index (BMI) influences pregnancy outcomes, its associations with RP are unclear. We aimed to examine associations between BMI, demographic and clinical factors, and RP using a nationally representative inpatient dataset. Methods This retrospective study analyzed data of women aged ≥18 years with delivery hospitalizations from the US Nationwide Inpatient Sample 2016–2020. RP was identified using the ICD‐10 codes. Included women were classified on the basis of BMI as non‐obese (<30.0 kg/m 2 ), obese (30.0–39.9 kg/m 2 ), and morbidly obese (≥40.0 kg/m 2 ). Weighted logistic regression analysis determined associations between study variables and RP occurrence. Results Among 3 590 940 delivery hospitalizations, 28 935 women (0.8%) had RP. Multivariable analysis identified advanced maternal age (adjusted odds ratio [aOR] = 1.046, 95% CI: 1.044–1.049), obesity (aOR = 1.18), morbid obesity (aOR = 1.25), polycystic ovary syndrome (PCOS) (aOR = 1.33), endometriosis (aOR = 2.28), smoking (aOR = 1.33), multiple pregnancy (aOR = 2.37), uterine surgery (aOR = 2.04), abortion (aOR = 1.43), and infertility (aOR = 1.87) as independent risk factors for RP. Cesarean delivery (vs. vaginal delivery) was significantly associated with a lower risk of RP (aOR = 0.14). Subgroup analyses confirmed consistent risk factors across age, prematurity, and PPROM, with multiple pregnancy, endometriosis, PCOS, obesity, and smoking remaining significant predictors. Conclusion Obesity is an independent risk factor for RP, and morbid obesity confers the highest risk. Study findings emphasize the need for patient‐focused obstetric management in high‐risk populations.