Whenwill, here's the study. There's also one on oral clefts, that finds the same thing. I've seen something that says 2 of 7 studies think there may be a link to clefts but 5/7 are to the contrary. In a sense it doesn't matter much, because supplementation is essential for neural tube reasons anyway. I mean, non-neural midlines aren't the issue spina bifida is. Maybe the bigger issue is why we don't automatically supplement bread, as I understand is done in the USA (?). Perhaps there is a reason I don't know of.
DS had one of the worst tongue-ties the surgeon (Mervyn Griffiths, who wrote the study the WHO now rely on in advising division - the procedure had fallen out of favour for some years before he began to perform it again, and in fact he was reported to the BMA by a couple of irate colleagues...) had ever seen, even after the failed initial cut. It turned out that the tie had been so severe that his tongue was restricted even after division, and only a few months of eating solids, and thus using the tongue constantly, altered that. For the first months of eating he had to use his hands to remove food he didn't want to eat - his tongue couldn't do it. He also has a double frenulum, so it looks like this: () under his tongue now, post-division. His father has a severe tongue tie too, which was never seen to. And I supplemented with folic acid before and during pregnancy, incidentally. It didn't stop it happening.
Obviously my own situation is just anecdotal and nothing more, but I am concerned to see women in this thread worrying and blaming themselves, when there is no strong evidence that they need to. I was folated to the gills, but it didn't help this. DS has a sacral dimple and a severe tt. So does his father. Don't rule out genetics, because one of the first things I was told was that if a parent has a tonguetie then the odds are about 1 in 4 that a baby will, too.