HealthDay News — In utero and early life exposure to traffic-related air pollution during pregnancy and the first year of life may increase autism risk, study results suggest.

Children with autism were more likely to live in homes in the highest quartile of car emission exposure during gestation (adjusted odds ratio 1.98; 95% CI: 1.20-3.31) and the first year of life (aOR 3.10; 95% CI: 1.76-5.57) compared with control children, Heather Volk, PhD, MPH, of the University of Southern California in Los Angeles, and colleagues reported in Archives of General Psychiatry.

Children with autism “were three times as likely to have been exposed during the first year of life to higher modeled traffic-related air pollution,” the researchers wrote.

Continue Reading

The association was strongest during late gestation and early life; however, the researchers were unable to “adequately distinguish a period critical to exposure.”

Volk and colleagues examined the relationship between traffic-related air pollution, air quality and autism in a case-control study involving 279 children with autism and 245 control children enrolled in the Childhood Autism Risks from Genetics and the Environment study in California.

Traffic-related air pollution exposure was estimated for each trimester of pregnancy, and the first year of life for each location identified from birth certificate data and reported residential history using data from the Environmental Protection Agency’s Air Quality System. Exposures to nitrogen dioxide, ozone, and particulate matter measuring less than 2.5 μm and 10 μm in aerodynamic diameter were included in the analysis.

Only particulate matter and nitrogen dioxide exposure were significantly tied to risk of autism, while there was no association seen between autism risk and ozone exposure, the researchers found.

Among pollutants, nitrogen dioxide exposure during the first year of life (aOR 2.06; 95% CI: 1.37-3.09) and throughout pregnancy (aOR 1.81; 95% CI: 1.23-2.65) was associated with a greater autism risk. First trimester exposure was associated with a nearly 50% increased risk of autism (aOR 1.47; 95% CI: 1.05-2.20). The risk was also increased during the second (aOR 1.62; 95% CI: 1.17-2.25) and third (aOR 1.64; 95% CI: 1.18-2.29) trimesters.

A greater than two-fold risks of autism during the child’s first year (aOR 2.12; 95% CI: 1.45-3.10) and throughout pregnancy (aOR 2.08; 95% CI: 1.93-2.25) was identified for particulate matter less than 2.5 μm. This risk was highest in the second (aOR 1.48; 95% CI: 1.40-1.57) and third trimesters (aOR 1.40; 95% CI: 1.11-1.77), but the researchers found no association between third trimester exposure and autism.

Particulate matter less than 10 μm had a significant association with risk of autism during the first year (aOR 2.14; 95% CI: 1.46-3.12), throughout pregnancy (aOR 2.17; 95% CI: 1.49-3.16), and during the first (aOR 1.44; 95% CI: 1.07-1.96), second (aOR 1.83; 95% CI: 1.35-2.47) and third trimesters (aOR 1.61; 95% CI: 1.20-2.14).

“Although additional research to replicate these findings is needed, the public health implications of these findings are large because air pollution exposure is common and may have lasting neurological effects,” the researchers wrote.

In an accompanying editorial, Geraldine Dawson, PhD, of the University of North Carolina at Chapel Hill, called for more research to examine how the interplay between genes and environmental risk factors during the prenatal and early postnatal periods increase the risk for autism spectrum disorders.


  1. Volk HE et al. Arch Gen Psychiatry 2012; doi:10.1001/jamapsychiatry.2013.266.
  2. Dawson G et al. Arch Gen Psychiatry 2012.