The population-based examination of the Norwegian Mother and Child Cohort Study (MoBa) assessed 85,176 children born between 2002-2008. Researchers evaluated the of folic acid intake of mothers from 4 weeks before to 8 weeks after the start of pregnancy, defined as the first day of the last menstrual period before conception.
At the end of follow-up, 270 children in the study sample had been diagnosed with autism spectrum disorders (ASDs): 114 with autistic disorder, 56 with Asperger syndrome, and 100 with PDD-NOS. In children whose mothers took folic acid, 0.10% (64/61,042) had autistic disorder, compared with 0.21% (50/24,134) in those unexposed to folic acid. The adjusted OR for autistic disorder in children of folic acid users was 0.61 (95% CI, 0.41-0.90). No association was found with Asperger syndrome or PDD-NOS, but power was limited. Similar analyses for prenatal fish oil supplements showed no such association with autistic disorder, even though fish oil use is associated with the same maternal characteristics as folic acid use.
These results led the study to conclude that use of prenatal folic acid supplements around the time of conception was associated with a lower risk of autistic disorder in the MoBa cohort. Although these findings cannot establish causality, they do support prenatal folic acid supplementation.
Researchers explained that while ethical considerations prohibit placebo-controlled randomized trials that eliminate folic acid, further observational studies of mothers who do and do not use supplements might be informative.