A recent study published in JAMA evaluated over 85,000 children born in 2002-2008 from the Norwegian Mother and Child Cohort Study.  The children ranged in age between 3.3 through 10.2 years after follow-up.  In mothers who took folic acid, 0.10% of children had autistic disorder compared to 0.21% of children whose mothers did not take folic acid.  No association was found between folic acid and risk of Asperger syndrome or unspecified autism disorder.  How often do you receive questions from your female patients about use of folic acid or other supplements prior to pregnancy?

See the article in JAMA.