Does pregnancy affect the thyroid and vice versa? will high levels cause the fetus any distress?

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.