It is better to have it treated as best as possible keep in the perfect range to much thyroid hormone can affect the baby
I was hyper when I was pregnant and my son has craniosynostosis I feel strongly that is what caused it. I was not told I was hyper nor treated I only know now from medical records.
http://findarticles.com/p/articles/mi_m0CYD/is_14_41/ai_n16621416/?tag=content;col1
http://www.cdc.gov/ncbddd/bd/keyfindings/thyroid.htm
From what I have read over the last two days with a pregnancy scare that is the best medication to go on during pregnancy. Hope this helps