Prenatal folic acid supplementation may reduce the risk of neural tube defects in children, but it is unclear whether it reduces other neurodevelopmental disorders. This study by Christine Roth, PhD, of the Norwegian Institute of Public Health was designed to explore the association between maternal prenatal folic acid supplementation and the risk of later onset of autism spectrum disorder (ASD) (autism, Aspergers syndrome, generalized developmental delay) in children. They found that folic acid supplementation before and after conception reduced the risk of autism. The paper was published in the latest online edition of the prestigious international journal JAMA 2013. The study sample was drawn from the Norwegian Population-based Mother-Child Cohort Prospective Study (MoBa). Subject children were born between 2002 and 2008 and followed up until March 31, 2012, with an age range of 3.3 to 10.2 years (mean, 6.4 years) and folic acid exposure from 4 weeks before pregnancy to 8 weeks after the start of pregnancy, counting from the first day of the last menstrual period before conception. The relative risk of ASDs was estimated using logistic regression analysis with 95 percent confidence intervals for the odds ratios (ORs). The analysis was corrected for maternal education level, year of birth, and number of births. The primary outcome of the trial was expertly diagnosed ASDs. The results showed that at the end of follow-up, 270 children in the study sample were diagnosed with ASDs: 114 with autism, 56 with Aspergers syndrome, and 100 with PDD-NOS. 0.10% (64/61,042) of infants born to mothers taking folic acid had autism, compared to 0.21% (50/24,042) in the group without folic acid exposure. 0.21% (50/24,134). The corrected OR for autism in children in the folic acid-exposed group was 0.61 (95% CI, 0.41-0.90). The researchers observed no such association for Aspergers syndrome or PDD-NOS. A similar analysis showed no association between prenatal fish oil supplementation and autism, although maternal characteristics were the same for fish oil use as for folic acid use. The study concluded that folic acid supplementation before and after conception reduced the risk of autism in the MoBa cohort. Although these findings were not causal, they still support the practice of prenatal folic acid supplementation.