Comment on “Maternal Prepregnancy Body Mass Index and Risk of Preterm Birth: The Role of Weight Gain during Pregnancy, Race, and Ethnicity”

We read with great interest the study by Sawadogo et al examining the relationship between prepregnancy body mass index (BMI), gestational weight gain, and preterm birth (PTB) across racial and ethnic groups.[1] The authors should be commended for utilizing an extensive U.S. natality dataset and for implementing stratified analyses by both weight gain and demographic subgroups, thus enriching the interpretability of BMI-related risk patterns. However, several statistical and clinical concerns merit clarification.

First, the use of logistic regression models across BMI categories stratified by five weight gain groups and seven race/ethnicity subgroups resulted in over 200 subgroup-specific odds ratios. However, no correction was applied for multiple comparisons, nor was the model fit assessed for subgroups with limited event counts (e.g., Native Hawaiian or Pacific Islander mothers with underweight BMI). This undermines the interpretive reliability of outlier odds ratios, particularly in obesity class III, where confidence intervals broaden despite statistical significance.[2]

Second, the study described a “J-shaped” association between BMI and PTB but did not validate this nonlinear pattern using restricted cubic splines or other formal modeling. Relying solely on categorical BMI bins imposes arbitrary cutoffs and may misrepresent inflection points, especially at higher BMI ranges, where body composition and metabolic risk diverge across ethnicities.[3] The omission of continuous BMI modeling precludes precision risk estimation needed for individualized counseling.

Third, while stratification by gestational weight gain improves granularity, gestational duration is inherently tied to weight gain.[4] Women delivering preterm have reduced time for weight accumulation, which may bias the associations. Although the authors acknowledge this limitation, no time-adjusted weight gain metrics (e.g., weight gain per week of gestation) were explored, despite their relevance to clinical decision making.

Finally, the finding that Asian mothers with obesity II exhibit markedly elevated PTB odds for 31 to 40 pounds of weight gain (odds ratio: 1.93) lacks context on the sample size, cultural dietary practices, or metabolic heterogeneity within Asian subpopulations. Without accounting for these modifiers, the implication of differential PTB vulnerability may overgeneralize the findings across a demographically diverse group.

Despite these limitations, the authors contribute valuable epidemiological insights and underscore the inadequacy of applying uniform BMI thresholds to all populations. Further refinement through individualized modeling and gestation-adjusted weight trajectories could enhance clinical applicability and inform race-conscious prenatal counseling in the future.

Authors' Contributions

P.S.: Conceptualization, methodology, and writing—original draft and review and editing.

R.M.: Writing—original draft and review and editing.

R.S.: Validation, supervision, project administration, and writing—original draft and review and editing.

Declaration of GenAI Use

During the writing process of this paper, the author(s) used Paperpal and ChatGPT-4o in order to perform language refinement, grammar enhancement, and stylistic refinement. The author(s) reviewed and edited the text and take(s) full responsibility for the content of the paper.

Publication History

Received: 04 August 2025

Accepted: 08 August 2025

Article published online:
29 August 2025

• References

• 1 Sawadogo W, Tsegaye M, Gizaw A, Newland H, Adera T. Maternal prepregnancy body mass index and risk of preterm birth: the role of weight gain during pregnancy, race, and ethnicity. Am J Perinatol 2025; 42 (11) 1389-1399
• 2 Lovasi GS, Underhill LJ, Jack D, Richards C, Weiss C, Rundle A. At odds: concerns raised by using odds ratios for continuous or common dichotomous outcomes in research on physical activity and obesity. Open Epidemiol J 2012; 5 (01) 13-17
• 3 Carter JL, Abdullah N, Bragg F. et al. Body composition and risk factors for cardiovascular disease in global multi-ethnic populations. Int J Obes (Lond) 2023; 47 (09) 855-864
• 4 Santos S, Eekhout I, Voerman E. et al. Gestational weight gain charts for different body mass index groups for women in Europe, North America, and Oceania. BMC Med 2018; 16 (01) 201