Maternal exposure to fine particulate air pollution linked to offspring autism risk

Autism Spectrum Disorder and Particulate Matter Air Pollution before, during, and after Pregnancy

Women who are exposed to high levels of air pollution during their third trimester of pregnancy may be twice as likely to have an autistic child, researchers from the Harvard School of Public Health (HSPH) found.

Air pollution image
HSPH study suggests that women who live in areas with high levels of fine particulate matter during pregnancy may be at significantly higher risk of having a child with autism, compared with pregnant women who reside in areas with low levels of fine particulate matter.


Autism spectrum disorder (ASD) is a developmental disorder with increasing prevalence worldwide, yet with unclear etiology.

To explore the association between maternal exposure to particulate matter (PM) air pollution and odds of ASD in her child.

We conducted a nested case-control study of participants in the Nurses’ Health Study II (NHS II), a prospective cohort of 116,430 US female nurses recruited in 1989, followed by biennial mailed questionnaires. Subjects were NHS II participants’ children born 1990-2002 with ASD (n=245), and children without ASD (n=1522) randomly selected using frequency matching for birth years. ASD was based on maternal report, which was validated against the Autism Diagnostic Interview-Revised in a subset. Monthly averages of PM with diameters ≤2.5 µm (PM2.5) and 2.5-10 µm (PM10-2.5) were predicted from a spatiotemporal model for the continental US and linked to residential addresses.

PM2.5 exposure during pregnancy was associated with increased odds of ASD, with an adjusted odds ratio (OR) for ASD per interquartile range higher PM2.5 (4.42 µg/m3) of 1.57 (95% CI: 1.22, 2.03) among women with the same address before and after pregnancy (160 cases, 986 controls). Associations with PM2.5 exposure 9 months before or after the pregnancy were weaker in independent models and null when all three time periods were included, while the association with the 9 months of pregnancy remained (OR=1.63; 95% CI: 1.08-2.47). The association between ASD and PM2.5 was stronger for exposure during the third trimester (OR=1.42 per inter-quartile range increase in PM2.5, 95% CI: 1.09, 1.86) than other trimesters (ORs 1.06 and 1.00) when mutually adjusted. There was little association between PM10-2.5 and ASD.

Higher maternal exposure to PM2.5 during pregnancy, in particular the third trimester, was associated with greater odds of her child having ASD.

Sources and more information
  • Autism Spectrum Disorder and Particulate Matter Air Pollution before, during, and after Pregnancy: A Nested Case–Control Analysis within the Nurses’ Health Study II Cohort, Environ Health Perspectives DOI:10.1289/ehp.1408133, 18 December 2014.
    Full study PDF.
  • Fine particulate air pollution linked with increased autism risk, Harvard School of Public Health, December 18, 2014.
  • Air Pollution Exposure in Pregnancy Linked to Autism in Study, Bloomberg News, December 18, 2014.
  • Maternal exposure to air pollution linked to offspring autism risk, MNT, December 18, 2014.
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