Unfortunately this podcast does not really provide an answer, but does highlight data published over the holidays which shows in another dataset, that the prevalence of autism seems to be leveling out, rather than continue to increase as it has done for the past several decades.  It isn’t the final word and clearly there may be exceptions, but now two national datasets have shown no further increase in autism prevalence in the last few years of looking.  Is it 1:68 as reported in one study or 1:39 in another?  Is it somewhere in between?  Still to early to say, but white boys seem to be the most likely to get a diagnosis no matter where you look.  Also, folic acid proves to show an effect on the probability of not just an autism diagnosis, but autism symptoms.  This is especially important for women taking anti epileptic medications for seizures and bipolar depression.  Welcome to 2018!

Here are links to the articles.  Some of them are open access!

https://www.ncbi.nlm.nih.gov/pubmed/29297068

https://www.cdc.gov/nchs/data/databriefs/db291.pdf

https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2667432

https://www.ncbi.nlm.nih.gov/pubmed/29279889