HMN 2026: How Air pollution during pregnancy shows varying effects by region

In the journal JAMA Network Open, ECHO Cohort Consortium researchers reported a negative association between weekly prenatal exposure to fine particulate air pollution and birth weight.

Low birth weight is a risk factor for neonatal mortality and a range of morbidities. Small infants born at term can face complications when fetal growth falls short for gestational age.

Fine particulate matter with an aerodynamic diameter less than 2.5 ?m is regulated as one of six criteria for air pollutants in the US. Animal and in vitro studies have linked exposure with placental inflammation, altered placental DNA methylation and protein expression, and impaired trophoblast invasion, patterns that can disrupt maternal-fetal nutrient transfer and fetal growth.

Several epidemiologic studies have reported negative associations between prenatal fine particulate matter exposure and birth weight. Pregnancy-average and trimester-average exposure measures can miss windows of susceptibility tied to developmental timing.

In the study, “Air Pollution Exposure and Birth Weight in the ECHO Cohort,” researchers conducted a retrospective analysis to identify windows of prenatal susceptibility to PM_2.5.

Analyses included 16,868 mother-newborn pairs from single live births between 37 and 42 weeks’ gestation. Participants were enrolled at one of 50 sites participating in the US Environmental Influences on Child Health Outcomes Cohort (ECHO). Daily high-resolution PM_2.5 estimates covered the contiguous US from 2003 through 2021 and linked residential exposure to geocoded addresses.

Signals early in gestation

Mean weekly PM_2.5 exposure measured 8.03 ?g/m³. Higher PM_2.5 exposure across pregnancy aligned with lower birth weight, even when comparing births at the same week of pregnancy.

Exposure during weeks 1–5 of pregnancy showed the strongest association. Weeks 3–5 of pregnancy stood out as the key time window for males. Females did not show a distinct time window association.

Exposure linked to lower birth weight, with regional exceptions

The association between prenatal air pollution exposure and birth weight differed by region. In the Northeast, results showed a negative association but no specific weeks stood out. Midwest results showed a negative association with a time window during weeks 12–18 of pregnancy. Southern sites showed a similar pattern, with a time window during weeks 3–9.

Western sites showed a small positive association with exposure, with two windows appearing at weeks 10–13 and 29–31.

Reported regional patterns did not match the early-pregnancy windows observed in the full sample or in males, only the full data revealed the connection.

The authors suggest that exposures occurring in the US Northeast, South, and Midwest may have stronger associations with birth weight than those occurring in the West, which could reflect regional differences in particle composition.

Researchers from the ECHO Cohort Consortium found that higher prenatal exposure to fine particulate air pollution aligned with lower birth weight in the overall sample, with the strongest signals during early pregnancy.

A key window appeared at weeks 1–5, and weeks 3–5 stood out for males. Most regions showed a negative association, but Western sites showed a small positive pattern that did not match the overall timing.

The findings show that a deeper interrogation of particulate source and higher resolution of confounding factors needs to take place in future studies.

The content is provided for information purposes only.