Pregnancy and Thyroid Disease

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Offline Munni

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Pregnancy and Thyroid Disease
« on: August 14, 2014, 09:56:33 AM »
How does pregnancy normally affect thyroid function?
Two pregnancy-related hormones—human chorionic gonadotropin (hCG) and estrogen—cause increased thyroid hormone levels in the blood. Made by the placenta, hCG is similar to TSH and mildly stimulates the thyroid to produce more thyroid hormone. Increased estrogen produces higher levels of thyroid-binding globulin, also known as thyroxine-binding globulin, a protein that transports thyroid hormone in the blood.

These normal hormonal changes can sometimes make thyroid function tests during pregnancy difficult to interpret.

Thyroid hormone is critical to normal development of the baby’s brain and nervous system. During the first trimester, the fetus depends on the mother’s supply of thyroid hormone, which comes through the placenta. At around 12 weeks, the baby’s thyroid begins to function on its own.

The thyroid enlarges slightly in healthy women during pregnancy, but not enough to be detected by a physical exam. A noticeably enlarged thyroid can be a sign of thyroid disease and should be evaluated. Thyroid problems can be difficult to diagnose in pregnancy due to higher levels of thyroid hormone in the blood, increased thyroid size, fatigue, and other symptoms common to both pregnancy and thyroid disorders.

Hyperthyroidism

What causes hyperthyroidism in pregnancy?

Hyperthyroidism in pregnancy is usually caused by Graves’ disease and occurs in about one of every 500 pregnancies.1 Graves’ disease is an autoimmune disorder. Normally, the immune system protects people from infection by identifying and destroying bacteria, viruses, and other potentially harmful foreign substances. But in autoimmune diseases, the immune system attacks the body’s own cells and organs.

With Graves’ disease, the immune system makes an antibody called thyroid-stimulating immunoglobulin (TSI), sometimes called TSH receptor antibody, which mimics TSH and causes the thyroid to make too much thyroid hormone. In some people with Graves’ disease, this antibody is also associated with eye problems such as irritation, bulging, and puffiness.

Although Graves’ disease may first appear during pregnancy, a woman with preexisting Graves’ disease could actually see an improvement in her symptoms in her second and third trimesters. Remission—a disappearance of signs and symptoms—of Graves’ disease in later pregnancy may result from the general suppression of the immune system that occurs during pregnancy. The disease usually worsens again in the first few months after delivery. Pregnant women with Graves’ disease should be monitored monthly.

How is hyperthyroidism in pregnancy diagnosed?

Health care providers diagnose hyperthyroidism in pregnant women by reviewing symptoms and doing blood tests to measure TSH, T3, and T4 levels.

Some symptoms of hyperthyroidism are common features in normal pregnancies, including increased heart rate, heat intolerance, and fatigue.

Other symptoms are more closely associated with hyperthyroidism: rapid and irregular heartbeat, a slight tremor, unexplained weight loss or failure to have normal pregnancy weight gain, and the severe nausea and vomiting associated with hyperemesis gravidarum.

A blood test involves drawing blood at a health care provider’s office or commercial facility and sending the sample to a lab for analysis. Diagnostic blood tests may include

    TSH test. If a pregnant woman’s symptoms suggest hyperthyroidism, her doctor will probably first perform the ultrasensitive TSH test. This test detects even tiny amounts of TSH in the blood and is the most accurate measure of thyroid activity available.

    Generally, below-normal levels of TSH indicate hyperthyroidism. However, low TSH levels may also occur in a normal pregnancy, especially in the first trimester, due to the small increase in thyroid hormones from HCG.

    T3 and T4 test. If TSH levels are low, another blood test is performed to measure T3 and T4. Elevated levels of free T4—the portion of thyroid hormone not attached to thyroid-binding protein—confirm the diagnosis.

    Rarely, in a woman with hyperthyroidism, free T4 levels can be normal but T3 levels are high. Because of normal pregnancy-related changes in thyroid function, test results must be interpreted with caution.

    TSI test. If a woman has Graves’ disease or has had surgery or radioactive iodine treatment for the disease, her doctor may also test her blood for the presence of TSI antibodies.

Source: http://www.endocrine.niddk.nih.gov/pubs/pregnancy/