The Association of Maternal Body Fat Distribution with Cesarean Delivery, Spontaneous Labor, and Perinatal Morbidity in Women with Body Mass Index ≥ 40 kg/m2

The objective of this study is to evaluate the relationship between late and third-trimester ultrasonographic/anthropometric measures of central adiposity and cesarean delivery in patients with body mass index (BMI) ≥ 40 kg/m2 and compare their predictive value to BMI alone. Prospective observational cohort study of patients receiving prenatal care and delivering at a single center (2018–2021). Individuals with nonanomalous singleton pregnancies and either BMI ≥ 40 kg/m2 or normal BMI between 32 and 360/7 weeks were included. In both BMI groups, individuals with delivery < 36 weeks, prior cesarean, and contraindication to vaginal birth were excluded. Patients underwent a study visit > 36 weeks at which 19 central adiposity measures (ultrasonographic and anthropometric), fat distribution indices (e.g., abdominal fat index [aFI]) and BMI (predictive exposures) were obtained by trained research and ultrasound personnel. For our primary analysis (BMI ≥ 40 kg/m2), the primary outcome was cesarean. Measurement exposures were evaluated at alpha = 0.05 using backward selection multivariable logistic regression to generate a parsimonious model. Receiver operator characteristic curves with area under the curve (AUC) assessed the model's predictive ability; AUCs for BMI and the parsimonious model were compared. A planned analysis included women with normal BMI. Of 611 individuals screened, 265 were eligible, 217 consented, and 201 met all study criteria and were analyzed: 149 with BMI ≥ 40 kg/m2 (mean BMI: 45.4 ± 5.2; cesarean rate: 21%). A model of maximum preperitoneal fat depth above the umbilicus, below umbilicus aFI, and subxiphoid aFI (all p < 0.05) was significantly more predictive of cesarean (AUC: 0.76; 95% confidence interval [CI]: 0.67–0.86) than BMI alone (AUC: 0.60; 95% CI: 0.49–0.71; p = 0.002). When analyzing the normal BMI group (n = 52), a six-measurement model had outstanding prediction (AUC: 0.97; 95% CI: 0.93–1.00)—exceeding BMI alone (AUC: 0.64; 95% CI: 0.49–0.78; p < 0.001). Select maternal ultrasonographic fat depth measurements near delivery have significantly more predictive ability than BMI alone for cesarean delivery in patients with BMI ≥ 40 kg/m2 and should be further explored in those with normal BMI.