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