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

Introduction

Maternal obesity is a well-established risk factor for adverse pregnancy outcomes, including gestational diabetes, hypertensive disorders of pregnancy, cesarean delivery, and both short- and long-term cardiometabolic morbidity for mother and offspring [1], [2], [3], [4]. Large observational studies and meta-analyses have consistently demonstrated graded increases in obstetric and neonatal risk with increasing body mass index (BMI) across diverse populations and healthcare systems [5], [6], [7].

National surveillance data based on birth certificates indicate that obesity among reproductive-aged women in the United States has increased steadily over several decades [8], [9], [10], [11]. While prior analyses documented rising obesity prevalence across states and racial and ethnic groups [9], [10], [11], [12], [13], [14], [15], [16], much of this literature emphasizes cross-sectional burden rather than longitudinal changes in the underlying BMI distribution. This approach may obscure population-level structural shifts, particularly the contraction of normal weight status as a decreasing proportion of women enter pregnancy within recommended BMI ranges [17]. From a perinatal epidemiology perspective, the declining prevalence of normal prepregnancy weight represents the erosion of a protective baseline rather than simply the accumulation of extreme BMI categories. We term this phenomenon the “vanishing normal weight”, a population-level trend where the healthy weight category shrinks not merely due to the expansion of one specific risk group, but as a systemic loss of the normative baseline.

An additional limitation of conventional surveillance is the uniform application of standard BMI thresholds. Substantial evidence indicates that Asian populations experience obesity-related metabolic dysfunction at lower BMI levels than White or Black populations due to differences in body composition and visceral adiposity [18], [19], [20], [21]. Consequently, the World Health Organization and national expert groups recommend lower BMI cut points for defining obesity in Asian populations to avoid underestimating metabolic risk [19], [20], [21], [22], [23].

The objective of this study was to examine national trends in prepregnancy BMI from 2016 through 2024 across major U.S. racial and ethnic groups. We utilized multiple complementary visual frameworks – interrogating absolute prevalence, relative growth, and threshold behavior – to reveal structural changes in maternal metabolic health over time.

Methods, study design and data source

We conducted a retrospective population-based analysis using publicly available Centers for Disease Control and Prevention (CDC) Natality data, including all live births in the United States from 2016 through 2024 [24]. Maternal race and ethnicity were obtained from birth certificate data and categorized into seven mutually exclusive groups: Non-Hispanic (NH) American Indian or Alaska Native, NH Asian, NH Black, NH Native Hawaiian or Other Pacific Islander, NH White, NH More than one race, and Hispanic of all races.

Results

The analysis included 32,726,128 live births in the United States from 2016 through 2024. Annual prevalence of prepregnancy obesity by maternal race and ethnicity is presented in Table 1 and Figure 1. By 2024, normal weight prevalence approached or fell below 50 % for all racial and ethnic groups except Asian mothers.

Figure 1:

Annual prevalence of prepregnancy obesity by maternal race and ethnicity, United States, 2016–2024. Annual prevalence trends of prepregnancy obesity. The solid black line represents the TOTAL population average. Obesity is defined as BMI ≥30.0 kg/m² for all groups except Asian mothers (BMI ≥25.0 kg/m²). The Asian trend line demonstrates a rapid ascent, crossing the trajectories of hispanic and multiracial mothers to approach the high-risk cluster of non-hispanic black and AI/AN populations. The x-axis ticks represent the study years 2016–2024; labels on the right indicate the final prevalence in 2024.

Across the study period, obesity prevalence increased in every racial and ethnic group. In 2016, obesity prevalence ranged from 24.0 % among Non-Hispanic White mothers to 44.9 % among Non-Hispanic Native Hawaiian or Other Pacific Islander mothers. By 2024, prevalence ranged from 29.5 % among Non-Hispanic White mothers to 51.6 % among Non-Hispanic Native Hawaiian or Other Pacific Islander mothers. Among Asian mothers, using an obesity threshold of BMI ≥25.0 kg/m², obesity prevalence increased from 29.7 % in 2016 to 41.4 % in 2024.

Relative changes in obesity prevalence between 2016 and 2024 are summarized in Table 2. Asian mothers experienced the largest relative increase (relative risk 1.39; 95 % CI 1.38–1.40). Relative increases were also observed among Hispanic mothers (RR 1.23; 95 % CI 1.23–1.24), Non-Hispanic White mothers (RR 1.23; 95 % CI 1.22–1.23), Non-Hispanic mothers of more than one race (RR 1.20; 95 % CI 1.19–1.22), Non-Hispanic Black mothers (RR 1.17; 95 % CI 1.16–1.17), Non-Hispanic Native Hawaiian or Other Pacific Islander mothers (RR 1.15; 95 % CI 1.11–1.18), and Non-Hispanic American Indian or Alaska Native mothers (RR 1.14; 95 % CI 1.12–1.17).

Longitudinal distributions of prepregnancy BMI categories by race and ethnicity are shown in Figure 2. Multidimensional comparisons of obesity prevalence in 2016 and 2024 are presented in Figure 3. Normal weight prevalence declined over time in all groups. Indexed trends in obesity prevalence, standardized to 2016 values, are shown in Figure 4. Absolute changes in normal weight prevalence relative to the 2016 baseline are displayed in Figure 5, demonstrating cumulative declines across all racial and ethnic groups. Changes in the proportion of births occurring among mothers with normal weight relative to the 50 % threshold are illustrated in Figure 6.

Figure 2:

Distribution of prepregnancy BMI categories by maternal race and ethnicity, United States, 2016–2024. Longitudinal trends in the prevalence of four BMI categories by maternal race and ethnicity: Underweight (<18.5 kg/m²), normal weight (18.5–24.9 kg/m²), overweight (25.0–29.9 kg/m²), and obesity (≥30.0 kg/m²). Standard BMI thresholds were applied for all groups except Asian mothers, for whom obesity was defined as BMI ≥25.0 kg/m² to reflect ethnicity-specific metabolic risk; consequently, the conventional “overweight” category (25.0–29.9 kg/m²) is subsumed into the “obesity” category for this population. Normal weight prevalence declined across all racial and ethnic groups over the study period.

Figure 3:

Expansion of prepregnancy obesity prevalence by maternal race and ethnicity, United States, 2016 vs. 2024. Radar plot illustrating the multidimensional expansion of the obesity epidemic. The inner grey polygon represents the prevalence in 2016, and the outer red polygon represents 2024. The complete engulfment of the 2016 area by the 2024 area indicates that risk has increased along every demographic axis without exception. The axis for Asian mothers (BMI ≥25.0 kg/m²) shows a significant outward expansion, reflecting the group’s 39 % relative increase in prevalence.

Figure 4:

Indexed trends in prepregnancy obesity prevalence by maternal race and ethnicity, United States, 2016–2024 (baseline 2016=100). Line graph standardizing the 2016 obesity prevalence to a baseline value of 100 for all groups to visualize the velocity of change. The solid black line represents the TOTAL population. The red line representing Asian mothers highlights the steepest trajectory of acceleration (index ∼139 in 2024), significantly outpacing the national average and groups with higher absolute burdens (e.g., NHOPI, black). This visualization isolates the rapidity of epidemiological transition independent of absolute prevalence.

Figure 5:

Absolute change in normal weight prevalence from 2016 baseline by maternal race and ethnicity, United States, 2016–2024. This figure tracks the absolute percentage point change in normal weight prevalence (BMI 18.5–24.9 kg/m²) relative to 2016. The solid black line represents the TOTAL population decline. Values below zero indicate cumulative decline in normal weight prevalence, or the systematic erosion of the healthy weight category. Asian mothers (red line) experienced the steepest descent, losing approximately 8.2 percentage points of normal weight prevalence by 2024, a rate of loss exceeding that of all other racial and ethnic groups.

Figure 6:

Trends in normal weight prevalence relative to the 50 % majority threshold by maternal race and ethnicity, United States, 2016–2024. The solid black line represents the total population average. Other lines represent specific racial/ethnic groups with distinct styles. The dashed horizontal line represents the 50 % critical threshold, below which births at a normal weight (BMI 18.5–24.9 kg/m²) cease to be the demographic norm. Trends indicate that for the majority of racial and ethnic groups, normal weight status is now a minority event. The Asian population exhibits a steep linear decline approaching the threshold possibly within the next 3–4 years.

Discussion

In this national population-based analysis of more than 32 million U.S. births from 2016 through 2024, prepregnancy BMI distributions shifted unfavorably across all racial and ethnic groups. These findings indicate a change in the metabolic profile of women entering pregnancy, characterized not only by rising obesity but by the systematic erosion of normal weight as the baseline condition. No single visualization adequately captures this transformation; however, when absolute prevalence, relative change, and threshold behavior are examined together, the loss of normal weight as the normative baseline becomes apparent.

Groups with historically high obesity prevalence, including Non-Hispanic Native Hawaiian or Other Pacific Islander, Non-Hispanic Black, and Non-Hispanic American Indian or Alaska Native mothers, continued to exhibit the highest absolute prevalence throughout the study period. This persistence aligns with prior national surveillance documenting entrenched disparities in prepregnancy obesity and related metabolic risk [9], [10], [11], [12], [13, [28], [29], [30]. Importantly, Figure 3 illustrates that between 2016 and 2024, obesity prevalence expanded across every racial and ethnic axis without exception.

A central finding of this study is the magnitude and velocity of change among Asian mothers when ethnicity-specific BMI thresholds are applied. Asian mothers experienced the largest relative increase in obesity prevalence between 2016 and 2024. Although absolute prevalence in 2024 remained lower than that of some high-burden groups, Asian mothers experienced the steepest absolute decline in normal weight prevalence over time. These results are consistent with extensive evidence that Asian populations develop metabolic dysfunction at lower BMI levels than other groups [18], [19], [20], [21], [22], [23], reinforcing the importance of applying ethnicity-appropriate cut points in obstetric surveillance.

The vanishing normal weight prevalence across all racial and ethnic groups represents a clinically meaningful shift with broad implications for perinatal risk [1], [2], [3], [4], [5], [6], [7]. Furthermore, this structural change must be viewed through the lens of the Developmental Origins of Health and Disease (DOHaD). Explicitly referencing Barker’s hypothesis, the maternal metabolic environment serves as a primary determinant of offspring physiology. The erosion of the normal weight baseline suggests that a growing proportion of the next generation is being exposed to an altered metabolic milieu in utero. These altered BMI trajectories may influence long-term offspring health, potentially increasing the population-level susceptibility to non-communicable diseases, including cardiovascular disease, diabetes, and cancer. Thus, the trends observed here likely underestimate the full public health impact, which may manifest intergenerationally.

As shown in Figure 6, normal weight status has fallen below the 50 % majority threshold for most groups, indicating that entry into pregnancy at a recommended BMI is no longer the norm. Prior studies have documented rising prepregnancy obesity [14], [15], [16], [17, 31], but the present analysis extends this literature by demonstrating that the contraction of the normal weight category is a defining feature of recent trends.

It is important to emphasize that while we use terms such as “metabolic deterioration” or “structural transformation” to describe these trends, the present study is descriptive in nature. We observed population-level prevalence shifts rather than individual physiological progression, and causal inference regarding the drivers of these trends is beyond the scope of this analysis. Furthermore, while we stratified by race and ethnicity, these unadjusted trends may also reflect concurrent shifts in maternal age, parity, socioeconomic status, and access to care, which were not controlled for in this descriptive overview.

This study has several strengths, including the use of a robust national dataset and consistent methodology. Limitations include reliance on self-reported prepregnancy height and weight, which may result in reporting bias and systematic underestimation of BMI. Additionally, the race and ethnicity categories utilized are based on birth certificate standards, which may possess limitations in accurately capturing multiracial identities or self-identification.

In summary, our study demonstrates a decisive and universal deterioration in prepregnancy metabolic health in the United States between 2016 and 2024. This deterioration is defined by the systematic vanishing of normal weight as the predominant condition at pregnancy entry. The rapid rise in obesity prevalence among Asian mothers when appropriate thresholds are applied highlights the limitations of conventional surveillance approaches. The ubiquity of these trends suggests that solutions likely lie in system-level and public health interventions rather than individual-level clinical mandates. Ultimately, these results underscore the need to refocus clinical and public health strategies toward the preconception period as well as throughout pregnancy and postpartum, with emphasis on early identification of metabolic risk and prevention across the life course [32], [33], [34], [35], [36].