I have an underactive thyroid, currently on the thyroxine for it. But I now been reading all these articles that it can cause premature birth. Is that for women who arent monitored and not on medication? And does it affect my baby being born big? My daughter was born 9 pound 1 and my thyroid was diagnosed after this so Im thinking I had problems back then. So many question I should be asking the dr but I keep forgetting!