Pregnant women who are exposed to high levels of pollution have a greater chance of giving birth to children on the autism spectrum, a new study has found.
The chance of a child being on the spectrum doubled in high pollution areas such as cities, compared to cleaner-air rural areas.
The research, conducted at Harvard University, was said to be the first large-scale national study of pollution on the brain development of fetuses.
The findings are published in the journal Environmental Health Perspectives.
"Our findings raise concerns," said lead author Andrea Roberts, a research associate in the Harvard School of Public Health Department of Social and Behavioral Sciences.
Depending on the pollutant, between 20 and 60 percent of women in high pollution areas had children with a condition on the autism spectrum, she added.
In the analysis, researchers studied 22,000 women who had children without the disorder, and more than 350 women with children who were on the spectrum. The spectrum mothers showed a marked tendency to live in areas of higher auto and industrial pollution.
Pollution levels were taken from data collected by the American Environmental Protection Agency.