Exposure to air pollutants fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) during pregnancy was associated with slightly higher behavior problem scores in preschool-aged children, even when PM_2.5 levels were below the current United States air quality standard, according to a new ECHO Cohort study led by Jiwon Oh, PhD, and Deborah Bennett, PhD, of the University of California, Davis.

Air pollution is common in many places, and pregnant women can be exposed to it where they live, work, and travel. Scientists think some air pollutants may affect a baby’s developing brain during pregnancy, which could later show up as differences in behavior. Using data from 8,370 pregnant women and their children from 28 ECHO Cohort Study Sites across 21 U.S. states and Puerto Rico, researchers looked at the association between exposures to common air pollutants like PM_2.5, NO₂, and ozone (O₃) during pregnancy and behavior problems in young children.

Key takeaways:

• Exposure to PM₅ and NO₂ in air pollution during pregnancy was associated with modest increases in childhood behavior problems, including externalizing behaviors (e.g., acting out, aggression, attention problems) and internalizing behaviors (e.g., anxiety, withdrawal, emotional reactivity) in preschool-aged children (1.5–5 years).
• Exposures in different “sensitive windows” during pregnancy showed different links to child behavior. First trimester PM₅ exposure was associated with higher externalizing behavior scores. Second trimester PM_2.5 exposure was associated with higher internalizing behavior scores. Third trimester NO₂ exposure was linked to higher internalizing and externalizing behavior scores.
• Ozone (O₃) exposure was not significantly associated with child behavior scores overall.
• Certain individual and community-level sources of stress like prenatal depression and childhood neighborhood opportunity (e.g., job opportunities, economic resources, socio-economic inequities, housing quality) influenced the association between prenatal exposure to air pollution and child behavior.

“Many ECHO pregnant women are exposed to PM_2.5 levels that exceed the current U.S. air quality standard,” said Dr. Bennett. “Further investigations are needed to determine whether this standard is sufficiently protective of child neurodevelopment.”

Future studies can help researchers understand if prenatal air pollution exposure continues to show an association with children’s behavior beyond early childhood. Researchers can also explore how other factors, such as stress, access to healthcare, housing conditions, and other environmental exposures, might influence the association between prenatal air pollution exposure and children’s brain development.

This collaborative research, titled “Prenatal exposure to nitrogen dioxide, fine particulates, and ozone in relation to child behavior: The Environmental influences on Child Health Outcomes (ECHO) Cohort,” was published in Environmental Science & Technology.