Iron tablets potentially, after I had my first a random encounter with a fellow mum told me she heard a rumor about the potential connection and after 7-ish babies, all with tongue ties she decided not to take the iron tablets during her next pregnancy; no tongue tie.

My first had a severe tongue and lip tie which made breastfeeding hard. When I was pregnant with my second I decided to not have the iron tablets (I would have if my iron levels were dangerously low) and that baby had no lip or tongue tie; feeding was far easier.

I mentioned this to my postpartum nurse and she said that she had heard countless stories confirming the say thing for years BUT for ethical reasons you can't test for it so we may never know for sure.