The correct answer is:

Check her thyroperoxidase antibody level

Educational Objective:

Distinguish human chorionic gonadotropin–mediated hyperthyroidism from Graves disease.

Key Points:

Human chorionic gonadotropin–mediated hyperthyroidism is a transient, mild hyperthyroidism that occurs early in approximately 10% to 15% of pregnancies; patients have no thyromegaly or goiter and thyroperoxidase antibodies are normal. The condition usually resolves by 20 weeks gestation without treatment. The emergency physician’s job is to exclude the diagnosis of Grave’s disease.

Explanation:

Human chorionic gonadotropin (hCG)–mediated hyperthyroidism is a transient, mild hyperthyroidism that occurs early in approximately 10% to 15% of pregnancies and is not due to intrinsic thyroid disease. hCG, which peaks during the first trimester, has the ability to stimulate the TSH receptor, resulting in elevated T4 levels and suppressed TSH concentrations.

In general, the symptoms consist of nausea and sometimes vomiting (and perhaps anxiety), resolving spontaneously by 20 weeks of gestation. The most severe form of hCG-mediated hyperthyroidism is hyperemesis, also known as transient hyperthyroidism of hyperemesis gravidarum.

Distinguishing this hCG-mediated hyperthyroidism (usually no treatment required) from Graves hyperthyroidism (treatment required) may be challenging; a key difference is that a patient with hCG-mediated hyperthyroidism will not have thyroperoxidase antibodies, whereas the person with Graves disease will have antibodies.

In addition, the person with Graves disease is more likely to have a goiter, and ultrasonography of the thyroid will show increased vascularity.

None of these (antibodies, goiter, increased vascularity) are present in the patient with hCG-mediated hyperthyroidism.

Nausea/vomiting are more pronounced with hCG-mediated hyperthyroidism than with Graves disease.

In some patients, serum TSH may remain suppressed or below normal after normalization of serum T4.

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