(294) Association between very elevated BMI and cesarean delivery in the United States

Elevated body mass index (BMI) is an established risk factor for cesarean delivery (CD), but the implications of BMI elevation beyond 40 kg/m² on CD risk are poorly described. Our aim was to describe the proportion of CD in the United States across a broad spectrum of BMI, focusing on people with BMI greater than 40.

Study Design:

This retrospective cohort study utilized the Epic Cosmos dataset. Pregnancies were included if they occurred between July 2018 and June 2025, had an available delivery summary, pre-pregnancy BMI was between 18.5 and 80 kg/m2, and were without history of prior CD. BMI was categorized as 18.5-24.9, 25.0-29.9, 30.0-39.9, 40.0-49.9, 50.0-59.9, 60.0-69.9, and 70.0-79.9. The proportion of pregnancies resulting in CD and the 95% confidence interval (CI) were calculated for each BMI category. Results were stratified by parity; and among nulliparous patients, additional stratification by gestational diabetes (GDM), pre-gestational diabetes (DM), and chronic hypertension (cHTN) according to the International Classification of Diseases codes was performed.

Results:

A total of 7,324,281 pregnancies were included, of which 19.5% resulted in CD. The probability of CD increased from 15.5% with BMI 18.5-24.9 to 49.2% for BMI 70.0-79.9 in a monotonic fashion (Figure 1a). Parity strongly impacted the probability of CD, with nulliparous patients at greater risk of CD (Figure 1b). Among nulliparous patients, GDM, pregestational DM, and cHTN were all associated with higher rates of CD across the range of BMI (Figures 2a-2b).

Conclusion:

Among pregnancies without history of CD, there is a monotonic relationship between BMI and CD risk, strongly influenced by parity. Comorbid conditions further increase CD risk. The average nulliparous patient with BMI >50 has >50% probability of CD, a risk that increases further with higher BMI or comorbidities. Studies are warranted to investigate indications for CD among these high-risk patients and to support individualized counseling regarding CD risk and delivery planning.