Question: "Is maternal use of prenatal vitamins associated with decreased risk for autism recurrence in siblings of children with autism spectrum disorder?" Answer: "Maternal prenatal vitamin intake during the first month of pregnancy may reduce ASD [autism spectrum disorder] recurrence in siblings of children with ASD in high-risk families." So that looks like a 'very possibly' then.
That was the long-and-short of the findings reported by Rebecca Schmidt and colleagues . Some notable names are included on the authorship list of the Schmidt paper who are no strangers to the idea that maternal prenatal vitamin use may very well impact on offspring risk of autism or ASD (see here and see here for examples).
The Schmidt study on this occasion relied on data from the MARBLES (Markers of Autism Risk in Babies: Learning Early Signs) study, an important longitudinal initiative originally designed to investigate "possible pre-natal and post-partum biological and environmental exposures and risk factors that may contribute to the development of autism." Yes, you read that right, that's 'biological and environmental' exposures and risk factors (see here)...
In this "prospective cohort study" younger brothers and sisters deemed to be at high-risk of autism (N=241) by virtue of their older sibling having been diagnosed with autism were the target participant group. Said group were followed from 6 months to around about their third birthday and developmentally assessed. Mums of the children were also asked about their vitamin use during pregnancy via interview. All the collected data was crunched and results presented.
"The prevalence of ASD was 14.1% (18) in children whose mothers took prenatal vitamins in the first month of pregnancy compared with 32.7% (37) in children whose mothers did not take prenatal vitamins during that time." As you can see, that is quite a stark [statistically significant] difference between the groups bearing in mind that around 25% of the total cohort were eventually diagnosed with autism (or at least met thresholds for a diagnosis based on the use of a gold-standard instrument). Authors also add that prenatal vitamin use did not seemingly impact on "other nontypical development" which included various other developmental 'outcomes'. They also reported that: "Children in the former maternal prenatal vitamin group also had statistically significantly lower autism symptom severity... and higher cognitive scores." This implies that even if such vitamin use did not 'halt' a/the pathway to an autism diagnosis in some, it might well have affected the presentation of their autism in terms of symptoms and intellectual functions (see here).
So an important question: what were the nutrients being supplemented that seemed to show such an effect? Well, as per that other previous research from Schmidt et al folic acid popped up again, as well as another important nutrient, iron (Fe) which she's also been previously interested in (see here).
As per some 'expert reaction' to the study (see here) there is a need for further research in this area before any sweeping generalisations are made. Ideally, I'd like to see Schmidt or others go further into the whole folate metabolism bit applied to autism (see here and see here) and what that means for supplementation levels in mums-to-be where offspring autism recurrence risk is potentially high. Indeed, whether folic acid is actually the ideal supplement for some pregnant mums (see here) is another potential route of investigation on the basis of what has previously turned up in 'some autism' (see here). By saying all that, I want to make it clear that I'm not giving anything that looks, sounds or smells like medical or clinical advice on this or any topic. The Schmidt findings also potentially tie into another area of autism research looking at the inter-pregnancy interval (IPI) with autism in mind (see here and see here). This, on the basis that words like 'depletion of micronutrients' have been banded around as being one possible explanation for the elevated risk of offspring autism correlating with a short IPI. Again, more study is indicated.
I try not to get too excited about new findings when it comes to autism because, inevitably, many end up falling by the wayside or being over-hyped. Given however the history of peer-reviewed science on the topic of pregnancy nutrition and risk of offspring autism, I'm inclined to think that there may be something quite special in the Schmidt findings and what directions they could eventually take with regards to both research and policy. Certainly when I read another study talking about siblings at 'high-risk' for autism, I'll be looking to see whether pregnancy nutrition has been considered as a potentially modifying variable...
28 February 2019: An addition. So, here I am talking about prenatal vitamin use and offspring autism risk and lo-and-behold, someone has just published a meta-analysis and systematic review of this topic . The conclusion: "the likelihood of ASD in offspring whose mothers used multivitamin supplements during the prenatal period was significantly reduced compared with that in offspring of mothers without such supplementation."
 Schmidt RJ. et al. Association of Maternal Prenatal Vitamin Use With Risk for Autism Spectrum Disorder Recurrence in Young Siblings. JAMA Psychiatry. 2019. Feb 27.
 Guo B-Q. et al. Maternal multivitamin supplementation is associated with a reduced risk of autism spectrum disorder in children: A systematic review and meta-analysis. Nutrition Research. 2019. Feb 24.