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Hyperthyroidism during pregnancy: Clinical manifestations, diagnosis, and causes

Douglas S Ross, MD
Section Editors
David S Cooper, MD
Charles J Lockwood, MD, MHCM
Deputy Editor
Jean E Mulder, MD


Overt hyperthyroidism (low thyroid-stimulating hormone [TSH], elevated free thyroxine [T4] and/or triiodothyronine [T3]) is relatively uncommon during pregnancy, occurring in 0.1 to 0.4 percent of all pregnancies [1,2]. The diagnosis of pregnant women with hyperthyroidism parallels that of nonpregnant women and men but presents some unique problems. The clinical manifestations, diagnosis, and causes of hyperthyroidism during pregnancy are presented here. The treatment of hyperthyroidism during pregnancy and other aspects of thyroid disease during pregnancy are discussed separately. (See "Hyperthyroidism during pregnancy: Treatment" and "Overview of thyroid disease in pregnancy".)


The diagnosis of thyroid disease during pregnancy requires an understanding of the changes in thyroid physiology and thyroid function tests that accompany normal pregnancy. These changes are reviewed briefly below and in more detail separately. (See "Overview of thyroid disease in pregnancy", section on 'Thyroid adaptation during normal pregnancy'.)

To meet the increased metabolic needs during a normal pregnancy, there are changes in thyroid physiology that are reflected in altered thyroid function tests. These changes include the following:

Thyroid hormone-binding globulin (TBG) excess results in high serum total T4 and total T3 concentrations but not high serum free T4 or free T3 concentrations.

High serum human chorionic gonadotropin (hCG) concentrations during early pregnancy and even higher concentrations in women with hyperemesis gravidarum or multiple pregnancies may result in transient subclinical or rarely overt hyperthyroidism.

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Literature review current through: Dec 2017. | This topic last updated: Jan 24, 2017.
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