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In a new study from California, children with an autism spectrum disorder were more likely to have mothers who lived close to fields treated with certain pesticides during pregnancy.

Proximity to agricultural pesticides in pregnancy was also linked to other types of developmental delay among children.

“Ours is the third study to specifically link autism spectrum disorders to pesticide exposure, whereas more papers have demonstrated links with developmental delay,” said lead author Janie F. Shelton, from the University of California, Davis.

There needs to be more research before scientists can say that pesticides cause autism, she told Reuters Health in an email. But pesticides all affect signaling between cells in the nervous system, she added, so a direct link is plausible.

California is one of only a few states in the U.S. where agricultural pesticide use is rigorously reported and mapped. For the new study, the researchers used those maps to track exposures during pregnancy for the mothers of 970 children.

The children included 486 with an autism spectrum disorder (ASD), 168 with a developmental delay and 316 with typical development.

Developmental delay, in which children take extra time to reach communication, social or motor skills milestones, affects about four percent of U.S. kids, the authors write. The Centers for Disease Control and Prevention estimates that one in 68 children has an ASD, also marked by deficits in social interaction and language.

In the new study, about a third of mothers had lived within a mile of fields treated with pesticides, most commonly organophosphates.