The vanishing normal weight: U.S. pregnancy trends by race and ethnicity, 2016-2024.

Abstract

Objectives: To characterize national trends in prepregnancy body mass index from 2016 to 2024 across U.S. racial and ethnic groups, with particular attention to normal weight prevalence at pregnancy entry.

Methods: We conducted a retrospective population-based analysis of 32,726,128 live births using CDC National Vital Statistics System Natality data from 2016 through 2024. Prepregnancy BMI was calculated from self-reported height and weight on birth certificates. Obesity was defined as BMI ≥30.0 kg/m² for all groups except Asian mothers, for whom BMI ≥25.0 kg/m² was applied per established ethnicity-specific metabolic risk thresholds.

Results: By 2024, normal weight prevalence had fallen below 50 % for all racial and ethnic groups except Asian mothers, who nonetheless demonstrated the steepest downward trajectory. Obesity prevalence increased steadily across all groups while normal weight declined universally. Non-Hispanic Native Hawaiian or Other Pacific Islander mothers had the highest absolute obesity prevalence at 51.6 %. Applying ethnicity-appropriate thresholds, obesity among Asian mothers reached 41.4 % - exceeding Non-Hispanic White and Hispanic mothers - representing the largest relative increase between 2016 and 2024.

Conclusions: Between 2016 and 2024, the U.S. obstetric population experienced broad metabolic deterioration characterized by rising obesity and erosion of normal weight as the normative baseline at pregnancy entry. Ethnicity-specific BMI thresholds reveal Asian mothers as a rapidly emerging high-risk population, underscoring the need for system-level interventions and recalibrated preconception metabolic strategies.