It is my understanding that you HAVE to take your thyroid meds while pregnant, the baby needs them too!
I had a miscarriage due to my thyroid, but that was before I was getting treatment for it, if I would have been on synthroid back then it may not have happened.
Call your doctor ASAP and keep your OB informed as well, get your levels checked evefry trimester is not more often.
Congrats!!! We are trying unsuccessfully to TTC, darn thyroid.