A new Norweigian study shows a possible link between folic acid supplementation and lower autism and autism-spectrum disorder. The study was published in JAMA in 2013. Folic acid was supplemented from 4 weeks before conception to 8 weeks afterward. Folic acid use during this time period is also know to decrease the risk of central nervous system defects (neural tube defects) in pregnancy and is the reason for universal recommendation for prenatal vitamins prior to and during pregnancy. The recommended supplementation for folic acid in a normal pregnancy is 400 to 800 mcg depending on the source.
From OB.Gyn. News, Mary Ann Moon, ACOG practice bulletin #33