FRESNO, Calif. — A new study released Monday suggests that pregnant women who live near agricultural fields where pesticides are sprayed are at increased risk of having a child with autism.

The study by the University of California, Davis, MIND Institute found mothers exposed to organophosphates had a two-thirds increased risk of having a child with autism.

And the risk was strongest when exposures occurred during the second and third trimesters of pregnancies, the research showed.

UC Davis is not the first to report a possible link between autism and agricultural pesticide exposure. Seven years ago a study based in California’s Central Valley showed an association – and the UC Davis researchers said their results strengthen the evidence and warrant caution.

Families living close to agricultural fields may want “to leave town or keep their children away or close the windows” on days when pesticides are being applied, said Dr. Irva Hertz-Picciotto, senior author of the report and professor and vice chair of the Department of Public Health Services at UC Davis.

UC Davis said the study, published online Monday in “Environmental Health Perspective,” used commercial pesticide application data from the California Pesticide Use Report, which shows what pesticides are applied, and where and when they are applied.

The research included four classes of pesticides: organophosphates, organochlorines, pyrethroids and carbamates. The pesticides are used on a variety of crops in the Valley.