Fetal alcohol spectrum disorder (FASD) is a
rather complicated thing (wiki) to diagnose. And in consequence both considerably underdiagnosed and misdiagnosed. So, like that other infamous spectrum thing, any careful attempt to measure changes in incidence during specific periods is likely to get horribly mixed up with diagnosis issues. But maybe some specific symptoms - that might be more routinely diagnosed - might appear to have increased during specific periods that can be associated with pregnancies during lockdown.
But there is a logical/statistical argument that if alcohol consumption markedly increased during a period, then some increase in FASD is inevitable. Not necessarily in the same proportion, but some increase seems very likely. In modern times, very many of the pregnant carefully avoid alcohol. So it might seem possible that all of the increase in consumption was in the non-pregnant. But we know that some proportion, probably a small proportion, of the pregnant are not so careful, for all sorts of reasons. Some because they are unaware they are pregnant; some because they can't or don't control themselves; some because they just don't care that much; some because they don't want to reveal they are pregnant; etc. And there is that unfortunate social pressure that just a little bit won't matter, we're celebrating, it's just this once, it's real champagne, do have a teensy-weensy top-up, that can't hurt.
So whilst it seems likely that the increase in alcohol consumption in the pregnant will be rather less than the average increase in alcohol consumption during that period, it seems statistically very likely that there must be some increase in alcohol consumption by the pregnant. Which will fairly inevitably lead to some increase in FASD.
But having made this observation, one goes, well what do we want to do with this information? It's what it is. Certain outcome conditions might have somewhat elevated incidence during a particular period. Most or all of these conditions can't be cured, only ameliorated. It probably doesn't matter very much to know that they might have been the result of FASD.