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Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment

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


The evaluation and treatment of pregnant women with hypothyroidism parallels that of nonpregnant women and men, but presents some unique problems. There are several important issues that must be considered when hypothyroidism occurs during pregnancy or when women with preexisting treated hypothyroidism become pregnant. The clinical manifestations, diagnosis, and treatment of hypothyroidism during pregnancy are reviewed here. Other aspects of thyroid disease during pregnancy are reviewed elsewhere. (See "Overview of thyroid disease in pregnancy" and "Hyperthyroidism during pregnancy: Clinical manifestations, diagnosis, and causes" and "Hyperthyroidism during pregnancy: Treatment".)


Clinical manifestations — The range of clinical symptoms of hypothyroidism during pregnancy is similar to those that occur in nonpregnant patients and may include fatigue, cold intolerance, constipation, and weight gain. Symptoms may be overlooked or attributed to the pregnancy itself. Many patients are asymptomatic. (See "Clinical manifestations of hypothyroidism".)

Laboratory findings — 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 an increase in thyroxine (T4)-binding globulin, which results in total T4 and triiodothyronine (T3) concentrations that are higher than in nonpregnant women. In addition, high serum human chorionic gonadotropin (hCG) levels during early pregnancy result in a reduction in first trimester serum thyroid-stimulating hormone (TSH) concentrations. (See "Overview of thyroid disease in pregnancy", section on 'Thyroid adaptation during normal pregnancy'.)

Because of the changes in thyroid physiology during normal pregnancy, thyroid function tests should be interpreted using trimester-specific TSH and T4 reference ranges for pregnant women. The upper limit of normal for TSH in the first trimester of pregnancy is approximately 2.5 mU/L (3.0 mU/L in the second and third trimesters) rather than 4.5 to 5.0 mU/L used by most laboratories. Total T4 and T3 levels during pregnancy are 1.5-fold higher than in nonpregnant women. Reference ranges for free T4 are method-specific, and trimester-specific reference ranges should be provided with the assay kits. (See 'Diagnosis' below and "Overview of thyroid disease in pregnancy", section on 'Trimester-specific reference ranges'.)

Pregnancy complications — Hypothyroidism can have adverse effects on pregnancy outcomes, depending upon the severity of the biochemical abnormalities.


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Literature review current through: Sep 2016. | This topic last updated: Feb 26, 2015.
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