A new study adds to evidence linking autism risk and prenatal exposure to air pollution. (Andre Chung/TNS)

A new study adds to evidence linking autism risk and prenatal exposure to air pollution. (Andre Chung/TNS)

Exposure to high levels of air pollution during pregnancy — particularly during later stages — may double a woman’s risk of having a child with autism, a new Harvard study suggests.

The research, which looked at the experiences of pregnant women across the country, found that the risk of a child developing autism increased proportionally as pregnant women were exposed to greater amounts of fine particulate matter in the air.

The findings published online Thursday in the journal Environmental Health Perspectives build on previous research associating autism and air pollution, researchers say.

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“The evidence base for a role for maternal exposure to air pollution increasing the risk of autism spectrum disorders is becoming quite strong,” said Marc Weisskopf, a senior author of the study and an associate professor at the Harvard School of Public Health. “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.”

For the study, researchers reviewed data from a long-term study tracking the health experiences of 116,000 nurses across the nation starting in 1989. Within that group, they focused specifically on the pregnancies of mothers of 245 children who were diagnosed with autism and 1,522 without the developmental disorder.

Researchers used information from the U.S. Environmental Protection Agency and other sources to measure levels of fine particulate matter air pollution in the areas where the nurses lived while pregnant.

Autism risk was most significantly associated with air pollution exposure during the third trimester of pregnancy, the study found.