19 Dec, 2014 10:04

Air pollution in late pregnancy elevates risk of autism – Harvard study

The chance of children developing autism doubles among mothers exposed to high levels of air pollution during late pregnancy, compared with those living in cleaner areas, a major US study reveals.

Scientists at Harvard School of Public Health have found that the impact of exposure to fine particulate matter emitted by fires, vehicles and power plants maximizes during an expectant mother’s third trimester. The findings come from monitoring women for more than two years before, during and after pregnancy.

Their research was published in Environmental Health Perspectives journal Thursday.

The results were based on data from the Nurses' Health Study II – commenced in 1989, it includes 116,430 women, who have been followed by biennial mailed questionnaires since their recruitment.

The researchers analyzed the locations where the women lived while pregnant and the local levels of particular types of pollution.

Afterwards, the prenatal histories of 245 children with autism spectrum disorder (ASD) were compared to 1,522 children who had no abnormalities in their development. All child participants were born from 1990 to 2002, and as usually occurs with this type of disorder, most of the autistic children were boys.

“Our data add additional important support to the hypothesis that maternal exposure to air pollution contributes to the risk of autism spectrum disorders,” Harvard epidemiologist Marc Weisskopf, lead author of the study, said in a statement. The greater the exposure, the greater the risk, he said.

The way living in polluted areas correlates to ASD has been examined in previous research, but this is the first study carried out across the entire United States.

A similar but less scaled study was conducted in 2010. It revealed the same trend: the risk of autism is twice as much among mothers-to-be living near highways.

Minuscule particles, emitted by vehicles – PM2.5, particles 2.5 micrometers in diameter or smaller – are covered with countless contaminants and are believed to penetrate cells, which, in its turn, can interfere with the brain’s development.

“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.”

Autism is generally linked to genetics, but the increasing spread of the disorder among US children made scientists look into environmental causes. According to the most recent data, reported by government scientists, in 2010 diagnoses rocketed to one in 68 children from one in 150 in 2000.

However, it is not clear whether such a rise in figures depends on a better diagnostics or other factors yet to be studied.

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