Glossary

Term · Pregnancy: Your Body

gestational transient thyrotoxicosis

Also: transient thyrotoxicosis of pregnancy, hCG-mediated thyrotoxicosis

A brief overactive thyroid pattern in early pregnancy, driven by the pregnancy hormone hCG. It usually settles by mid-pregnancy without treatment.

In plain words

Gestational transient thyrotoxicosis is a short period of signs in early pregnancy. The thyroid itself is not diseased. The pregnancy hormone stimulates the thyroid and lowers the body's own signal. Blood tests show a low TSH and a raised free T4. Symptoms can include a fast heartbeat, nausea, , or feeling jittery. These are easy to mistake for or for anxiety. The pattern usually fades as hCG levels fall, often by the middle of pregnancy. It is different from Graves disease, which is an autoimmune condition. Clinicians check thyroid tests in people with severe nausea, which is one reason this pattern comes up.

The deeper version

Gestational transient thyrotoxicosis is biochemical hyperthyroidism in the first half of pregnancy, with suppressed TSH and elevated free T4 or T3 in the absence of thyroid autoimmunity. Human chorionic gonadotropin, which shares structural homology with TSH and stimulates the TSH receptor, is the principal driver. Its peak near the end of the first trimester corresponds with the nadir of TSH. Thyrotropin receptor antibodies are absent or low. Clinical signs overlap with hyperemesis, anxiety, and normal pregnancy. Management is generally supportive, and antithyroid treatment is reserved for significant clinical disease, according to the American Thyroid Association guidelines (Stagnaro-Green and colleagues, 2011). The controversy is how to separate this pattern from early Graves disease, and whether mild biochemical hyperthyroidism in the first trimester affects fetal outcomes.

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Sources

  • Stagnaro-Green A and colleagues (American Thyroid Association) — Guidelines for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid, 2011
  • Glinoer D — The regulation of thyroid function in pregnancy: pathways of endocrine adaptation from physiology to pathology. Endocrine Reviews, 1997

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