There is no problem with a mother taking Synthroid when she is pregnant and nursing. I just had a mom deliver that I had in this situation. We discovered her low thyroid after her first delivery when she was having trouble with milk supply. After the thyroid level returned low we supplemented her and then her supply improved. Since the first pregnancy she has continued on the hormone and she had no problem during the pregnancy and so far afterwards. I have checked the T4 level a little more often then I usually do since her levels and needs could change with the pregnancy. In her case they did not however.
Jon Ahrendsen MD FAAFP