Mothers who were exposed to pesticides during pregnancy have high risk of having children with autism, new study suggests. 

Previous research has shown that pesticides raise birth-defect risk in children. The current study by researchers with the UC Davis MIND Institute has found that living near an area where pesticides are used on a commercial scale also leads to a an increased risk of  having a child with autism spectrum disorder. The risk was especially high in women who were exposed to pesticides during second and third trimester.

Children diagnosed with Autism Spectrum Disorder suffer from several developmental disabilities. The condition leads to poor social and behavioral skills in children.  

The present study looked at the link between different types of pesticides- organophosphates, pyrethroids and carbamates- and their effects on autism risk.

"This study validates the results of earlier research that has reported associations between having a child with autism and prenatal exposure to agricultural chemicals in California," said lead study author Janie F. Shelton, a UC Davis graduate student who now consults with the United Nations.

"While we still must investigate whether certain sub-groups are more vulnerable to exposures to these compounds than others, the message is very clear: Women who are pregnant should take special care to avoid contact with agricultural chemicals whenever possible," said Shelton in a news release.

The study was based on data from 1,000 participants in the Northern California-based Childhood Risk of Autism from Genetics and the Environment (CHARGE) Study. The study includes children with autism, other developmental disorders and children with no known health problems. A majority of the participants lived in the Sacramento Valley, Central Valley and the greater San Francisco Bay Area.

Researchers obtained data on pesticide exposure from different parts of California. The team then matched pesticide levels near the homes of the participants to autism incidence.

Data association showed that pregnant women who lived in areas with high pesticide levels had increased odds of having a child with autism or other developmental delays.

About a third of CHARGE study participants lived within 1.25 to 1.75 kilometers of commercial pesticide application sites, researchers said.

 "We mapped where our study participants' lived during pregnancy and around the time of birth. In California, pesticide applicators must report what they're applying, where they're applying it, dates when the applications were made and how much was applied," Irva Hertz-Picciotto, a MIND Institute researcher and professor and one of the study authors. "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."

The fetal brain is much more vulnerable to toxins in the environment than adult brain, which might explain the developmental issues in children of mothers who were exposed to harmful chemicals during pregnancy, researchers said.

Among the pesticide studied, Organophosphates was associated with an increased risk of autism while Carbamates were linked to developmental delays. Exposure to Pyrethroids during conception or in the third trimester was associated with a moderate rise in autism risk.

The study is published in the journal Environmental Health Perspectives.