source: Graves' Disease & Thyroid Foundation
Hypothyroidism During Pregnancy
At first, your baby relies completely on tiny amounts of thyroid hormone that enter its circulation from your own blood. Hypothyroidism in a newborn baby or young child may lead to permanent mental retardation and growth impairment. It is therefore important that your thyroid hormone levels stay well within the normal range during your pregnancy. If you are already taking thyroid hormone, your TSH should be checked as soon as you become pregnant, with follow up tests completed every 6–12 weeks throughout your pregnancy.
Hyperthyroidism During Pregnancy
Some women who develop Graves’ disease will do so while they are pregnant. The chances of miscarriage and stillbirth rise if hyperthyroidism goes untreated, and the overall risks to you and your baby further increase if the disease persists late in pregnancy. Therefore, significant hyperthyroidism should be treated.
Since radioactive iodine can destroy the baby’s thyroid, the treatment of choice for an overactive thyroid diagnosed during pregnancy is anti-thyroid medication. Of the two available drugs, propylthiouracil (PTU) is usually preferred early in pregnancy.