Pregnant women, who are exposed to chemical pesticides, face a two-thirds heightened risk of having a child with autism spectrum disorder or other developmental delays, according to a new study by the University of California, Davis.

Researchers said that the effect was stronger when exposures occurred during the second and third trimesters of the pregnancy. They said that crop chemicals prohibit brain development in unborn children.

Advocates said that when dangerous chemicals can harm the brains and nerves of insects, it is not surprising to see similar results in humans. The building blocks of life are common in both humans and insects.

"If it were my family, I wouldn't want to live close to where heavy pesticides are applied," Researcher Irva Hertz-Picciotto said in a press release.

For the study, researchers analysed almost 1,000 mothers and their proximity to pesticides.

The researchers found that mothers, who lived within a mile from fields that were sprayed with common pesticides called organophosphates, were 60 percent likely to have a child with autism. Plus, women who were exposed to chemicals during their last three months of pregnancy were twice as likely to have an autistic child as others.

Among the pesticides, chlorpyrifos tripled the risk in women when exposed halfway through their pregnancy.

Researchers said that pesticides caused damages to an unborn child's brain as it may be especially vulnerable.

The research comes amid rising rates of autism.

"This research is of great concern when one considers the reliance of UK agriculture on pesticides and what appears to be a similarly large increase in autism here as in the US," said Elizabeth Salter Green, the director of campaign group CHEM Trust, Daily Mail UK reports.

Some were not convinced with the findings.

"Parents of children with autism are more likely to show autistic-like traits," said Dr Geoff Bird, of the Institute of Psychiatry at King's College London. "It may be that parents of autistic children prefer to live in less densely populated places which just happen to be closer to farms which just happen to use pesticides."

The finding is published in the journal Environmental Health Perspectives.