Thyroid hormones during pregnancy

Hi y’all, I’m studying for Step 1 right now and I always get the arrow pushing questions wrong for questions about changes to thyroid hormones during pregnancy. Can someone help me understand or point me to a good resource?

Total T3/T4 increases bc there’s more TBG during pregnancy… but why does free T3/T4 stay the same? Shouldn’t it go down because they’re being bound? And what happens to TSH?