Overall, the most common cause (80-85%) of maternal hyperthyroidism during pregnancy is Graves’ disease (see ) and occurs in 1 in 1500 pregnant patients. In addition to other usual causes of hyperthyroidism (see ), very high levels of hCG, seen in severe forms of morning sickness (hyperemesis gravidarum), may cause transient hyperthyroidism. The diagnosis of hyperthyroidism can be somewhat difficult during pregnancy, as 123I thyroid scanning is contraindicated during pregnancy due to the small amount of radioactivity, which can be concentrated by the baby’s thyroid. Consequently, diagnosis is based on a careful history, physical exam and laboratory testing.
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Graves’ disease may present initially during the first trimester or may be exacerbated during this time in a woman known to have the disorder. In addition to the classic symptoms associated with hyperthyroidism, inadequately treated maternal hyperthyroidism can result in early labor and a serious complication known as pre-eclampsia. Additionally, women with active Graves’ disease during pregnancy are at higher risk of developing very severe hyperthyroidism known as thyroid storm. Graves’ disease often improves during the third trimester of pregnancy and may worsen during the post partum period.
Thyroid disease in pregnancy - Wikipedia
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The effect of maternal hypothyroidism on the baby’s brain development is not as clear. Untreated severe hypothyroidism in the mother can lead to impaired brain development in the baby. This is mainly seen when the maternal hypothoidism is due to iodine deficiency, which also affects the baby However, recent studies have suggested that mild brain developmental abnormalities may be present in children born to women who had mild untreated hypothyroidism during pregnancy. At this time there is no general consensus of opinion regarding screening all women for hypothyroidism during pregnancy. However, some physician groups recommend checking a woman’s TSH value either before becoming prenant (pre-pregnancy counseling) or as soon as pregnancy is confirmed. This is especially true in women at high risk for thyroid disease, such as those with prior treatment for hyperthyroidism, a positive family history of thyroid disease and those with a goiter. Clearly, woman with established hypothyroidism should have a TSH test once pregnancy is confirmed, as thyroid hormone requirements increase during pregnancy, often leading to the need to increase the levothyroxine dose. If the TSH is normal, no further monitoring is typically required. This issue should be discussed further with your health care provider, particularly if you are contemplating pregnancy. Once hypothyroidism has been detected, the woman should be treated with levothyroxine to normalize her TSH and Free T4 values (see ).