Air Pollution Exposure in Early Pregnancy Lowers Birth Weight of Male Infants: JAMA
A new study published in the Journal of the American Medical Association found that exposure to fine particulate air pollution during the earliest weeks of pregnancy may significantly lower birth weight, particularly among male infants, which highlights the importance of protecting expectant mothers from polluted air during critical developmental windows.
This study analyzed data from nearly 17,000 mother–newborn pairs enrolled across 50 sites in the nationwide Environmental Influences on Child Health Outcomes (ECHO) Cohort between 2003 and 2021. Unlike earlier studies that averaged air pollution exposure across the entire pregnancy, this investigation examined week-by-week exposure to fine particulate, PM 2.5.
Using advanced machine-learning models to estimate daily residential exposure levels, this study mapped pollution exposure for each week of pregnancy. They then applied Bayesian distributed lag interaction models to determine when during gestation PM2.5 exposure most strongly affected fetal growth, measured by birth weight for gestational age (BWGA) z scores.
The findings revealed a strong negative relationship between prenatal PM 2.5 exposure and fetal growth. Despite the average weekly pollution levels being relatively low, the study found that higher exposure was associated with a measurable reduction in BWGA scores.
The most sensitive window emerged very early in pregnancy, during weeks one through five, when vital processes such as implantation and early organ formation occur. This early vulnerability was especially pronounced among male fetuses, which suggests biological differences in how male and female fetuses respond to environmental stressors.
Mothers living in the Northeast, Midwest, and South experienced stronger negative associations between pollution exposure and fetal growth compared to other regions. In the Midwest, the most sensitive window occurred between weeks 12 and 18, while in the South, it appeared earlier, which indicated that local pollution sources, climate, and population factors may influence risk.
The participant pool was diverse in race, ethnicity, and geography, strengthening the relevance of the findings across different U.S. populations. Average birth weight across the cohort was just over 3,400 grams, but even small population-wide decreases in birth weight are associated with increased risks of infant illness, developmental delays, and chronic disease later in life. Overall, this study highlights the importance of identifying “windows of susceptibility” during pregnancy.
Source:
Cowell, W., Hsu, H.-H. L., Just, A. C., Kloog, I., Coull, B. A., Wilson, A., Hipwell, A. E., Karagas, M. R., Gilliland, F. D., Padula, A. M., Carroll, K. N., Kerver, J. M., Ghassabian, A., Camargo, C. A., Jr, Dabelea, D., Koinis-Mitchell, D., D’Sa, V., Abul, M. H., Braun, J. M., … Smith, L. M. (2025). Air pollution exposure and birth weight in the ECHO cohort. JAMA Network Open, 8(12), e2551459. https://doi.org/10.1001/jamanetworkopen.2025.51459
