A new study has strengthened the link between exposure to fine particulate matter in the air during pregnancy and the risk of a child developing autism. The link was particularly strong when the exposure occurred during the third trimester, and the risk increased when the amount of particulate matter increased. Raanan Raz of Harvard University is lead author on the paper, which was published in Environmental Health Perspectives.
These results build on several previous studies that have found a link between the risk of developing autism and exposure to environmental factors such as fine particulate matter during early childhood. This, however, is the first study to collect data across the United States, focusing on exposure to particulate matter smaller than 2.5 microns during pregnancy. As a comparison, particles of dust typically range from 2.5-10 microns in diameter. However, there was not much of a correlation between autism risk and larger particles of this size.
The researchers analyzed data from 116,000 pregnant women from all 50 states who gave birth as far back as 1989. Of the resulting children, 245 were diagnosed with autism spectrum disorder. Their prenatal exposure to particulate matter was compared to that of 1,522 developmentally typical children, who served as controls. The levels of prenatal exposure were determined based on where the expecting mothers recorded their residence before, after, and during each trimester of pregnancy. The researchers then used air quality data from the EPA for each of the corresponding times and locations. Exposure to high levels during the third trimester conferred the greatest amount of risk.
“Our data add additional important support to the hypothesis that maternal exposure to air pollution contributes to the risk of autism spectrum disorders,” senior author Marc Weisskopf said in a press release. “The specificity of our findings for the pregnancy period, and third trimester in particular, rules out many other possible explanations for these findings.”
Ultimately, they discovered that expecting mothers who lived in areas with high levels of particulate matter would give birth to children with a risk of developing autism that was twice as high as their counterparts that lived in areas with fewer airborne particles. The results also showed that exposure prior to and following pregnancy did not contribute to risk.
“The evidence base for a role for maternal exposure to air pollution increasing the risk of autism spectrum disorders is becoming quite strong,” Weisskopf concluded. “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.”
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