Air Pollution During Pregnancy linked to Lower Birth Weight, With Regional Variations
A new study reveals a concerning link between exposure to fine particulate air pollution during pregnancy adn lower birth weight, with the most critical window of vulnerability occurring in the early stages of gestation. Researchers from the ECHO Cohort Consortium,publishing in JAMA Network Open on december 29,2025,found that the impact of air pollution varied significantly depending on the region of the United States.
Low birth weight is a well-established risk factor for both neonatal mortality and a range of health problems in infants. Even babies born at term can experience complications due to low birth weight.
previous animal and laboratory studies have suggested that PM2.5 exposure can disrupt placental function, altering DNA methylation and protein expression, and impairing nutrient transfer to the developing fetus. Several prior epidemiological studies have also indicated a negative association between PM2.5 and birth weight, but this new research delves deeper into the timing of these effects.
Researchers conducted a retrospective analysis of data from 16,868 mother-newborn pairs, examining births between 37 and 42 weeks’ gestation. Participants were enrolled through 50 sites participating in the US Environmental Influences on Child Health Outcomes Cohort (ECHO). The study utilized daily, high-resolution PM2.5 estimates from 2003 through 2021, linking exposure levels to the residential addresses of participants.
The analysis revealed that higher weekly PM2.5 exposure throughout pregnancy correlated with lower birth weight, even when comparing births occurring in the same week. Though, the strongest association was observed during the first five weeks of pregnancy. Notably, weeks three through five appeared particularly critical for male infants, while no distinct timing window emerged for females.
The impact of prenatal air pollution exposure also differed by region. In the northeast, a negative association was observed, but without a specific critical timeframe. Midwest sites showed a negative association linked to exposure during weeks 12-18 of pregnancy. Southern sites exhibited a similar pattern, with a key window between weeks 3-9.
Interestingly, Western sites showed a small positive association between PM2.5 exposure and birth weight, with two windows of potential impact at weeks 10-13 and 29-31. This regional variation was unexpected, and researchers noted that the early-pregnancy windows observed in the overall sample and in males were not reflected in the Western data.
“These findings suggest that the composition of particulate matter may differ regionally,leading to varying effects on fetal growth,” explained a senior researcher involved in the study.The authors hypothesize that the differences may be due to variations in the sources and chemical makeup of PM2.5 across the country.
the ECHO Cohort Consortium’s research confirms a link between higher prenatal PM2.5 exposure and lower birth weight, with early pregnancy being a particularly sensitive period. The study underscores the need for further investigation into the sources of particulate matter and the complex interplay of factors influencing birth outcomes. Future studies should focus on a more granular analysis of pollutant sources and a more thorough assessment of potential confounding variables.
More data: Whitney Cowell et al, Air Pollution Exposure and Birth Weight in the ECHO Cohort, JAMA Network Open (2025).DOI: 10.1001/jamanetworkopen.2025.51459
Journal information: JAMA Network Open
Key medical concepts:
- Birth Weight
- infant,Low Birth Weight
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