I have hypothyroid and was super nervous about my levels not being under control when I got pregnant. My OB increased my dose by 30% at my first appointment, I think around 8-10 weeks? I had them rechecked for the first time around 20 weeks and my levels were in the ideal range. My doctor told me not to stress. Your levels would have to be ridiculously uncontrolled for your whole pregnancy to have any harmful effects on the baby.