Prenatal exposure to certain pesticides may boost a child’s risk of autism by 60 percent, new research suggests. (Shutterstock)

A new study is adding to evidence that prenatal exposure to pesticides may significantly increase a child’s risk of autism.

Children born to mothers who lived within a mile of fields and farms where certain chemical pesticides were applied during pregnancy were at a two-thirds higher risk of autism or developmental delay, researchers found.

The risk was greatest during the second and third trimesters, according to findings published online Monday in the journal Environmental Health Perspectives.

For the study, researchers looked at more than 1,000 children in California whose mothers responded to questions about where they lived just before and during pregnancy. The addresses were cross-checked with detailed state records on agricultural chemical applications which included information on what types of chemicals were used, where, when and in what quantity.

“What we saw were several classes of pesticides more commonly applied near residences of mothers whose children developed autism or had delayed cognitive or other skills,” said Irva Hertz-Picciotto of the University of California, Davis MIND Institute who worked on the study.

One-third of the mothers lived within a mile of a chemical application site during the time studied, researchers said. In some cases, a mother’s proximity to a chemical spray directly correlated to greater or weaker odds of autism.

Kids born to mothers exposed to organophosphates were 60 percent more likely to have autism, the study found. Pyrethroids were also associated with an increased risk of autism, especially when the exposure occurred late in pregnancy, and carbamates were linked to developmental delay.

Researchers said the findings highlight the importance of reducing chemical exposure as much as possible around expectant mothers and young children, though they said other factors are also at play when it comes to autism and developmental delay.