The authors also looked separately at exposure to folic acid and to multivitamins and reported reductions in risk of autism spectrum disorder (ASD) for both, before and during pregnancy (relative risks are for comparisons with children of unexposed mothers in the same interval):
The authors note that the reduction in the risk of ASD in offspring after maternal exposure to folic acid and multivitamin supplements remained after adjusting for the presence of vitamin deficiency in the mother, and that further studies are needed to understand the underlying (potentially modifiable) mechanisms.
The say that their results are consistent with those of a Norwegian birth cohort study, but that they were not replicated in Danish studies on maternal use of folic acid and multivitamin supplements. They note their results should be interpreted with caution due to a number of limitations, including possible residual confounding, limited sample size, lack of information on the indication for the supplements, exposure misclassification, and lack of information on the mothers’ folate levels.
The NICE guideline on antenatal care for uncomplicated pregnancies (CG62) discusses nutritional supplements. It is recommended that women take 400mcg folic acid every day whilst trying for a pregnancy and up until they are 12 weeks pregnant, to help prevent neural tube defects. A daily vitamin D supplement is also recommended, to ensure that adequate vitamin D stores are maintained during pregnancy and whilst breastfeeding. The guideline does not recommend the routine use of any other nutritional supplements during pregnancy and warns that vitamin A supplementation (intake above 700 micrograms) might be teratogenic and should therefore be avoided.