With autism prevalence on the rise, research is increasingly citing exposure to air pollution as a contributing factor. A new study adds to the evidence, suggesting 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.

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Exposure to high levels of fine particulate matter during pregnancy – especially in the third trimester – may significantly increase offspring autism risk, researchers find.

The research team – including senior author Marc Weisskopf, associate professor of environmental and occupational epidemiology at Harvard School of Public Health in Boston, MA – found that offspring autism risk was highest among women exposed to fine particulate matter (PM) in the third trimester of pregnancy.

They publish their findings in the journal Environmental Health Perspectives.

In recent months, Medical News Today have reported on numerous studies indicating a link between air pollution and autism. In June, a study from the University of California-Davis claimed women who live in close proximity to pesticide sites during pregnancy are two thirds more likely to have children with autism or other developmental delays than women who live far away from such sites.

And in October, we reported on a study led by researchers from the University of Pittsburgh Graduate School of Public Health in Pennsylvania, which found that children with autism were more likely to have been exposed to air pollutants in early life and during mother’s pregnancy than those without the condition.

But this latest study, the researchers say, is the first US-wide study to investigate the link between maternal exposure to fine PM – particles up to 2.5 micrometers in diameter, often found in smoke and haze – and offspring autism risk.

To reach their findings, Weisskopf and colleagues analyzed 116,430 women and their children from 50 states who were part of the Nurses’ Health Study II, which began in 1989.

The researchers recorded where the women lived during their pregnancy, and they used data from the US Environmental Protection Agency and other sources to determine the levels of fine PM the women would have been exposed to before pregnancy, throughout each trimester and after pregnancy.

The team identified 245 children who were diagnosed with autism during the study period, as well as 1,522 children without autism to act as controls.

The results of the study revealed that women exposed to high levels of fine PM during pregnancy were almost twice as likely to have a child with autism than women who were exposed to low levels of fine PM. What is more, offspring autism risk was found to be highest among women exposed to high levels of fine PM in the third trimester of pregnancy.

No association was found between exposure to fine PM before or after pregnancy and offspring autism risk, and maternal exposure to larger-sized particles – 2.5 or more – appeared to have little influence on a child’s risk of autism.

Commenting on the team’s findings, Weisskopf says:

Our data add additional important support to the hypothesis that maternal exposure to air pollution contributes to the risk of autism spectrum disorders. The specificity of our findings for the pregnancy period, and third trimester in particular, rules out many other possible explanations for these findings.”

Autism prevalence has increased by 30% in the last 2 years alone, from 1 in 88 children affected by the disorder in 2012 to 1 in 68 children in 2014.

Weisskopf notes that there is an increasing amount of strong evidence for a link between maternal exposure to air pollution. “This not only gives us important insight as we continue to pursue the origins of autism spectrum disorders,” he adds, “but as a modifiable exposure, opens the door to thinking about possible preventative measures.”

MNT recently reported on a study published in the journal Nature Communications, which suggests inflammation may be a marker of autism.