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Diagnosing Hyperthyroidism and Graves' Disease During Pregnancy

How Hyperthyroidism and Graves' Disease Are Diagnosed in a Pregnant Woman

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Updated March 19, 2009

Diagnosing Hyperthyroidism and Graves' Disease During Pregnancy

Diagnosis of hyperthyroidism during pregnancy can be complicated

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Physical symptoms are often the first sign of hyperthyroidism in pregnancy. This is not an easy way to diagnose the condition, however, because some common symptoms of hyperthyroidism -- for example anxiety, fatigue, heat intolerance, and heart palpitations -- may be similar to symptoms of normal pregnancy.

But a thorough clinical thyroid exam can help pinpoint certain symptoms that are highly suggestive of hyperthyroidism, including goiter (an enlarged thyroid), eye symptoms like a stare, or bulging of the eyeball (known as ophthalmopathy), and weight loss.

The diagnosis of hyperthyroidism in pregnant women should be based primarily on a Thyroid Stimulating Hormone (TSH) blood test value of less than 0.01 mU/L and also a high free T4 value. If TSH is low, and Free T4 is normal or slightly elevated, Free T3 may also be measured, as high Free T3 can help confirm a diagnosis of hyperthyroidism.

Because hormonal changes in pregnancy can cause hyperthyroid blood tests -- without any clinical symptoms of hyperthyroidism -- borderline hyperthyroid TSH levels in pregnancy should not automatically lead to a diagnosis of hyperthyroidism. They may in fact be indicative of other forms of hyperthyroidism in pregnancy -- transient gestational transient thyrotoxicosis, and transient hyperthyroidism of hyperemesis gravidarum -- that were discussed in the article on signs and symptoms of hyperthyroidism in pregnancy.

Once actual clinical hyperthyroidism is established, determining the cause in a pregnant woman can be difficult because during pregnancy, doctors don't use the typical diagnostic tests for Graves' disease such as the radioactive iodine uptake test, or nuclear scanning, because of the serious harm these tests potentially pose to a developing baby.

But Graves' disease is the most common cause of an overactive thyroid in a pregnant woman, so to confirm diagnosis, thyrotropin receptor-stimulating antibodies (TSHR-SAb) -- also sometimes referred to as thyroid stimulating immunoglobulins -- should be measured. These antibodies are positive in most patients with Graves' disease, so this blood test can be used to diagnose Graves' disease during pregnancy.

Sources:

American College of Obstetricians and Gynecologists (ACOG). "Guideline: Thyroid disease in pregnancy." Washington (DC): 2002 Aug. 10 p. ACOG Practice Bulletin No. 37. Online

Braverman, MD, Lewis E., and Robert D. Utiger, MD. Werner and Ingbar's The Thyroid: A Fundamental and Clinical Text. 9th ed., Philadelphia: Lippincott Williams & Wilkins (LWW), 2005.

Ross, Douglas. "Diagnosis and treatment of hyperthyroidism during pregnancy." UpToDate.  Accessed: February 2009.

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