MONDAY, June 23, 2014 (HealthDay News) -- Pregnant women who live within a mile of spaces where commercial pesticides are applied appear to have an increased risk of having a child with autism, a new study suggests.

The risk that a child would develop autism appeared to be highest for women who lived near farms, golf courses and other public spaces that were treated with pesticides during the last three months of their pregnancies.

"Many of these compounds work on neurons. When they work on the insect, they're dealing with the nervous system of the insect and basically incapacitating it," said study author Irva Hertz-Picciotto, an environmental epidemiologist at the MIND Institute at University of California, Davis.

In adults, the brain is protected from many chemical exposures thanks to special filters that prevent many substances from crossing from the blood into the brain.

Hertz-Picciotto says that in young children, this blood-brain barrier isn't fully formed, which may allow pesticides to reach vulnerable nerve cells just as they are making vital connections to each other.

While the association between possible pesticide exposure and autism is interesting, an expert not involved in the research pointed out that it has a major flaw.

Because the study looked back in time, researchers weren't able to collect blood or urine samples to directly measure pesticide exposures. And they looked at risks associated with four different classes of chemicals.

"So this study cannot pinpoint specific substances as a culprit," said Philippe Grandjean, an adjunct professor of environmental health at Harvard School of Public Health in Boston, "Also, they cannot relate to specific levels of exposure, and they have not taken into account the possible contribution by residues in food," he said.

As a result, he said, the link reported in this study is weak.

Results of the study were released online on June 23 in the journal Environmental Health Perspectives.

One in 68 children is now diagnosed with autism, according to the U.S. Centers for Disease Control and Prevention. Autism is a disruption in normal brain development that generally appears within the first three years of a child's life.