The surprising thing to me in this research is the comparison of effectiveness in timing of the vitamin. Differences in rates of autistic children born (as diagnosed when five-year olds) was only significantly less in those mothers taking the prenatals during the first month of pregnancy.
By the second month, there was no difference in autism between the groups. So by the time many mothers find out they are pregnant, particular if the pregnancy was not planned, taking a prenatal vitamin is not effective in this regard- though it may be helpful in covering other nutritional needs during this time.
On an academic note, the last doctor who I observed in private practice is a self-taught enthusiast of using neurotransmitter and biochemistry knowledge in her clinical practice. She often tests for and uses targeted nutritional supplementation for women with MTHFR gene variants as it is disproportionately higher in women. Autism is one issue correlated with this gene defect; others are depression, anxiety, cardiovascular disease and some neurological diseases.
Genetic variants are not usually life sentences, but under the influence of a whole host of environmental influences. The realm of genetics if vastly fascinating to me, so please write with any medical genetics questions and I will look into writing up a little something on it. Thank you for reading!