Yes, both ways. Levels of thyroid binding protein increase in pregnancy and levels of T4 are higher than during the non-pregnant state. Both hypothyroid and hyperthyroid states impair fertility.
Yes and yes. The thyroid gland increases in size and function during pregnancy. Hyperthyroidism, if not controlled can be serious for mother and fetus. The mother may experience palpitations, pre-eclampsia, pre-term labor, thyroid storm and placental abruption (separation of the placenta from the uterine wall). The fetus can be growth restricted, miscarried, still-born and have thyroid dysfunction.