Doctors advise pregnant women to take 400 micrograms of folic acid every day.
It's a proven method of reducing babies' risk for serious birth defects, like spina bifida.
Now there's an apparent added benefit.
Researchers in Norway followed 85,000 children for six years.
They found women who took folic acid supplements before they got pregnant and during the first trimester lowered their babies' risk of developing autism by 40-percent.
Experts in the field call this link between nutrition and autism a landmark finding, but it's just one piece of a complicated puzzle of genetic and environmental factors that influence autism development.
"This does not prevent autism. There were women in this study who took prenatal folic acid and went on to have a child affected with autism," points out Dr. Alycia Halladay of Autism Speaks.
Our food supply is fortified with folic acid, but experts say many women may not be getting enough in their diet to make a difference.
They also say there's no downside to taking the supplements.
"To me, this is a no-brainer. It's a win-win proposition," says Dr. Max Wiznitzer. "It's good for the mother, it's good for the fetus, and you can't ask for anything better than that."
In addition to supplements and fortified breads and cereals folic acid is found naturally in dark green, leafy vegetables.