I had to have my thyroid 75% removed in my mid-twenties. I took Synthroid at first, and have been on the generic Levoxyl for years.
I had 3 children in my 30's.
During each pregnancy my OB (for the 1st) and midwife (for the 2nd and 3rd) drew blood monthly to monitor my thyroid levels. The worked with my endocrinologist (sending him the lab results monthly) so that he was aware of my levels throughout my pregnancy.
My 3 children are 6, 4 and 2. They are all perfectly healthy and normal. I was told that the risk was if my thyroid levels were off - that could cause birth defects and problems, that's why they monitor you so closely.
Perhaps your doctor misunderstood you - or made an error.
My experience is Levoxyl is perfectly safe. Your body NEEDS IT during pregnancy to PREVENT problems.
*** UPDATE*** if you are uncomfortable with your OB, you can switch doctors any time during your pregnancy. Literally, anytime! Go ahead and meet with her and see how the first meeting goes. Ask as many questions as you can. Decide from there. It seems like I went in early for blood tests in part to check my thyroid levels (it's been almost 4 years since I had an intitial prenatal check so I could be wrong). I'd go ahead and keep your appointment.
Jessica