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/m 2 for all groups except Asian mothers, for whom BMI ≥25.0 kg/m 2 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.