Poor Air Quality in Third Trimester and Autism

A new study adds to the evidence that maternal exposure to air pollution during pregnancy may be a contributing factor in the development of autism in children.

Researchers found that children born to pregnant women who were exposed to fine particulate matter during the third trimester had a higher risk for autism.

Key Points:

- Exposure to certain air pollution during the third trimester was associated with an increased risk of autism.  

- Particulate matter air pollution of 2.5 µm or less in diameter was the type of air pollution most associated with autism.

The findings were published in the journal Environmental Health Perspectives.

"Our data add additional important support to the hypothesis that maternal exposure to air pollution contributes to the risk of autism spectrum disorders," said Marc Weisskopf, associate professor of environmental and occupational epidemiology at Harvard School of Public Health and senior author of the study, in a news release. "The specificity of our findings for the pregnancy period, and third trimester in particular, rules out many other possible explanations for these findings."

The study relied on data from the Nurses’ Health Study II and information from the US Environmental Protection Agency. The researchers focused on particulate matter air pollution consisting of 2.5 µm in diameter or smaller. They found that exposure to particulate matter of this size (diameter, 2.5 µm or less) was significantly associated with autism during pregnancy. But exposure to the same pollution before and after pregnancy did not have the same association with a subsequent autism diagnosis for the child.

The greatest risk appeared to be tied to exposure during the third trimester. In addition, the authors reported that there was little association found between air pollution from larger-sized particles (those between 2.5 µm and 10 µm) and autism.

"The evidence base for a role for maternal exposure to air pollution increasing the risk of autism spectrum disorders is becoming quite strong," Weisskopf said. "This not only gives us important insight as we continue to pursue the origins of autism spectrum disorders, but as a modifiable exposure, opens the door to thinking about possible preventative measures."