This week a bunch of new studies came out that focused on changes in probability of having a child with autism after folic acid consumption during pregnancy. Moderate consumption folic acid and slightly elevated levels of plasma folate during pregnancy has now been shown in at least half a dozen scientific studies to reduce the chance of that child to be later diagnosed with autism. This is not a prevention effect, but a reduction in probability. There are enough studies on this question for a Chinese group to have organized them, put their data together, reanalyze them together and conclude that this is a real thing. If this was an effect seen after say, drinking battery acid, maybe it might require more consideration to recommend to the community. However, taking folic acid during pregnancy is something medical doctors are recommending pregnant women do anyway.
Want to learn more? Here are the studies:
Swedish Study: https://www.ncbi.nlm.nih.gov/pubmed/28978695
Denmark Study: https://www.ncbi.nlm.nih.gov/pubmed/28946926