Researchers in Israel studied 45,300 children born between Jan. 1, 2003 and Dec. 31, 2007, also looking at survey data that indicated whether their mothers were prescribed multivitamin and folic acid supplements.
The children were followed from birth to Jan. 26, 2015.
What researchers found: Those mothers who got either or both of the supplements during pregnancy had an estimated 73 percent lower chance of having a baby with an autism spectrum disorder than women who were not prescribed one or both of these supplements.
Of the children in the study, 572 were diagnosed with autism.
"Maternal exposure to folic acid and/or multivitamin supplements before pregnancy was statistically significantly associated with a lower likelihood of ASD in the offspring compared with no exposure before pregnancy," researchers said. "Maternal exposure to folic acid and/or multivitamin supplements during pregnancy was statistically significantly associated with a lower likelihood of ASD in offspring compared with no exposure during pregnancy."
The study's authors said, however, that their results "require cautious interpretation given several limitations" and that future studies were needed to replicate the findings.
Dr. Jennifer Ashton, ABC News' chief medical correspondent, said today that this study raises "interesting questions" about preconception and prenatal nutritional status and the resultant association with autism.
"At this time, general consensus is that there is not one singular cause of autism, but more likely multiple causative factors, however, these findings do reflect a positive association with maternal preconception and prenatal intake of folic acid/prenatal vitamins and a reduced risk of having a baby with autism," Ashton said. "While we need to show biologic causation to definitively reinforce this link, these findings serve as a reminder of the importance of preconception and prenatal nutrition."
"It is crucial, however, to not allow these findings to have negative social impact on mothers who have children with autism by blaming them in any way for this outcome, since obviously there are plenty of mothers who did consume adequate preconception and prenatal folic acid, and had an offspring with autism anyway," she said. "We need more research."
The study was published in The Journal of the American Medical Association Psychiatry.