My lovely fertility doctor, the late Dr. Alan Beer , was TOTALLY ahead of his time, and people in the medical community gave him SO much grief for it. For one thing, he advocated a preconception TSH (thyroid stimulating hormone--common test of thyroid function) of less that 2 (5 is considered "normal"). I usually feel best a 1.5 or below, so this was great news. But I remember one of my HARVARD endocrinologists yelling at me, saying I was going to have heart problems, etc, and refusing to let my TSH get lower than 5...while trying to get me to take Clomid!
I found a new endo and now feel pretty good, because he follows Dr. Beer's theories. Interestingly, I worked in a clinic for pregnant women and saw all sortsr of charts of women who DIDN'T have thyroid disease, a LOTS of them, in fact most, had TSH of around 0.5. So there you go.
Anyway, now a study tracking women with so-called "subclinical hyperthyroidism" had the same pregnancy outcomes as people without disease. So don't be afraid to push your endo to get your levels down to where YOU feel better. And also, consider taking "natural" (e.g., Armour) thyroid rather than synthetic. The Harvard endo and I battled about this, too. Glad I'm not with her anymore. Also, the natural thyroid doesn't have dyes in it...yay.