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Am J Perinatol 2025; 42(11): 1389-1399
DOI: 10.1055/a-2494-2080
Original Article

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

Wendemi Sawadogo 
1   Department of Public Health, College of Human and Health Services, Southern Connecticut State University, new Haven, Connecticut
2   Department of Epidemiology, School of Population Health, Virginia Commonwealth University, Richmond, Virginia
,
Medhin Tsegaye
2   Department of Epidemiology, School of Population Health, Virginia Commonwealth University, Richmond, Virginia
,
Andinet Gizaw
2   Department of Epidemiology, School of Population Health, Virginia Commonwealth University, Richmond, Virginia
,
Hunter Newland
2   Department of Epidemiology, School of Population Health, Virginia Commonwealth University, Richmond, Virginia
,
Tilahun Adera
2   Department of Epidemiology, School of Population Health, Virginia Commonwealth University, Richmond, Virginia
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Funding None.
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Abstract

Objective

Preterm birth (PTB) is one of the leading causes of infant and neonatal mortality. Prepregnancy body mass index (BMI; kg/m2) has been linked to PTB but the evidence of this association by weight gain during pregnancy, race, and ethnicity is limited. This study aimed to assess the association between maternal prepregnancy BMI and PTB stratified by weight gain during pregnancy, race, and ethnicity.

Study Design

The U.S. natality data from 2017 to 2021 were used. In this analysis, we included mothers who had a live singleton birth and available data for prepregnancy BMI, gestational age at birth, weight gain during pregnancy, race, and ethnicity. Logistic regression models were used to assess the association between prepregnancy BMI categories and PTB stratified by weight gain during pregnancy, race, and ethnicity.

Results

A total of 17,311,509 singleton live births were included of which 1,393,889 (8.05 %) were PTBs. After adjusting for confounders, compared with normal prepregnancy BMI mothers (18.5–24.9), those with underweight BMI (<18.5) were at increased odds of PTB regardless of weight gain during pregnancy, race, and ethnicity. However, for mothers with a prepregnancy BMI above the normal weight (≥25), the association between prepregnancy BMI and PTB differs by weight gain during pregnancy, race, and ethnicity. Asian mothers with obesity II (35.0–39.9) had 93% (odds ratio [OR] = 1.93, 95% confidence interval [CI]: 1.62–2.30) increased odds of PTB for weight gain during pregnancy of 31 to 40 pounds. Their White, Hispanic, and Black counterparts experienced lower odds of PTB for similar weight gain during pregnancy (White: OR = 1.56, 95% CI: 1.51–1.60; Hispanic: OR = 1.48, 95% CI: 1.41, 1.54; and Black: OR = 1.22, 95% CI: 1.17–1.27).

Conclusion

Mothers with underweight BMI were at increased risk of PTB regardless of weight gain during pregnancy, race, and ethnicity. However, the association between high prepregnancy BMI and PTB varied by weight gain during pregnancy, race, and ethnicity.

Key Points

  • The association between prepregnancy BMI categories and PTB had a “J” shape, with lower odds in the normal weight group.

  • Low prepregnancy BMI was associated with increased risk of PTB regardless of weight gain during pregnancy, race, and ethnicity.

  • The association between high prepregnancy BMI and PTB varies by weight gain during pregnancy, race, and ethnicity.

Keywords

pregnancy - body mass index - obesity - weight gain during pregnancy - race - ethnicity - preterm birth

Availability of Data and Materials

The datasets analyzed in this study are publicly available at: https://www.cdc.gov/nchs/data_access/vitalstatsonline.htm .


Authors' Contributions

Conceptualization, W.S. and T.A. methodology, W.S., M.T., A.G., H.N., and T.A. software, W.S. formal analysis, W.S. and T.A. writing—original draft preparation, W.S. writing—review and editing, W.S., M.T., A.G., H.N., and T.A. All authors have read and agreed to the published version of the manuscript.


Supplementary Material



Publikationsverlauf

Eingereicht: 14. August 2024

Angenommen: 01. Dezember 2024

Accepted Manuscript online:
02. Dezember 2024

Artikel online veröffentlicht:
28. Dezember 2024

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