The Norway study suggests there’s an additional reason to take extra folate if you are preparing to have a baby and while you are pregnant.
The B-group vitamin is known to prevent neural tube defects, such as spina bifida.
Published in the Journal of the American Medical Association, the study showed children born to women who took folic acid supplements four weeks before, to eight weeks after, conception appeared to be at a lower risk of autism.
More than 85,000 Norwegian children took part in the study and were born between 2002 and 2008.
Researchers found one in 1,000 babies born to women who reported taking folic acid early in pregnancy had autism, compared to about two in 1,000 of those whose moms didn't take folic acid.