Pregnant women living near fields sprayed with pesticides have an increased chance of having a child with autism spectrum disorder. Aqua Mechanical / Flickr

Taking the recommended amount of folic acid around the time of conception could reduce pesticide-related autism risks in children.

Women who took 800 micrograms or more of folic acid at conception had a significantly lower chance of having a child with autism than those who didn't, a study in the journal Environmental Health Perspectives finds.

The study looked at 296 children between the age of 2 and 5 who had been diagnosed with autism spectrum disorder, and 220 who hadn't. Their mothers were interviewed about their exposure to pesticides during pregnancy, and their folic acid and Vitamin B consumption. This data was coupled with information on the amount of agricultural spraying in the regions near the mother's addresses.

"We found that if the mom was taking folic acid during the window around conception, the risk associated with pesticides seemed to be attenuated," said study author Rebecca Schmidt, of the University of California, Davis, in a statement.

"Mothers should try to avoid pesticides. But if they live near agriculture, where pesticides can blow in, this might be a way to counter those effects."

Folic acid has been known to be important during pregnancy for many years. It is added to breakfast cereals and other food to increase women's intake. Folic acid plays a crucial role in DNA regulation, turning genes on or off, repairing DNA and making more of it.

"These are all really important during periods of rapid growth when there are lots of cells dividing, as in a developing foetus," Schmidt said. "Adding folic acid might be helping out in a number of these genomic functions."

Either being exposed to pesticides during pregnancy or having a low folic acid intake around conception increased mothers' likelihood of having a child with autism. But the combination of the two had the strongest effect.

"It would be better for women to avoid chronic pesticide exposure if they can while pregnant," Schmidt said.