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Thyroid Disease in Pregnancy

The thyroid diseases hyperthyroidism and hypothyroidism are relatively common in pregnancy and important to treat. The thyroid is an organ located in the front of your neck that releases hormones that regulate your metabolism (the way your body uses energy), heart and nervous system, weight, body temperature, and many other processes in the body.

During pregnancy, if you have pre-existing hyperthyroidism or hypothyroidism, you may require more medical attention to control these conditions during pregnancy, especially in the first trimester. Occasionally, pregnancy may cause symptoms similar to hyperthyroidism in the first trimester. If you experience palpitations, weight loss, and persistent vomiting, you should contact your physician.

Untreated thyroid diseases in pregnancy may lead to premature birth, preeclampsia (a severe increase in blood pressure), miscarriage, and low birth weight among other problems. It is important to talk to your doctor if you have any history of hypothyroidism or hyperthyroidism so you can be monitored before, and during pregnancy and your treatment adjusted if necessary.  

Symptoms of Hyperthyroidism and Hypothyroidism in Pregnancy

Symptoms of hyperthyroidism may mimic those of normal pregnancy, such as an increased heart rate, sensitivity to hot temperatures, and fatigue. Other symptoms of hyperthyroidism include the following:

  • Irregular heartbeat
  • Nervousness
  • Severe nausea or vomiting
  • Slight tremor
  • Trouble sleeping
  •  Weight loss or low weight gain for a typical pregnancy

Symptoms of hypothyroidism, such as extreme tiredness and weight gain, may be easily confused with normal symptoms of pregnancy. Other symptoms include:

  • Constipation
  • Difficulty concentrating or memory problems
  • Sensitivity to cold temperatures
  • Muscle cramps

Causes of Thyroid Disease in Pregnancy
The most common cause of maternal hyperthyroidism during pregnancy is the autoimmune disorder Grave’s disease. In this disorder, the body makes an antibody (a protein produced by the body when it thinks a virus or bacteria has invaded) called thyroid-stimulating immunoglobulin (TSI) that causes the thyroid to make too much thyroid hormone.

The most common cause of hypothyroidism is the autoimmune disorder known as Hashimoto’s thyroiditis. In this condition, the body mistakenly attacks the thyroid gland cells, leaving the thyroid without enough cells and enzymes to make enough thyroid hormone. 

Diagnosis of Thyroid Disease in Pregnancy
Hyperthyroidism and hypothyroidism in pregnancy are diagnosed based on symptoms, physical exam, and blood tests to measure levels of thyroid-stimulating hormone (TSH) and thyroid hormones T4, and for hyperthyroidism also T3

Treatment of Thyroid Disease in Pregnancy
For women who require treatment for hyperthyroidism, an antithyroid medication that interferes with the production of thyroid hormones is used. This medication is usually propylthiouracil or PTU for the first trimester, and — if necessary, methimazole can be used also, after the first trimester. In rare cases in which women do not respond to these medications or have side effects from the therapies, surgery to remove part of the thyroid may be necessary. Hyperthyroidism may get worse in the first 3 months after you give birth, and your doctor may need to increase the dose of medication. 

Hypothyroidism is treated with a synthetic (manmade) hormone called levothyroxine, which is similar to the hormone T4 made by the thyroid. Your doctor will adjust the dose of your levothyroxine at diagnosis of pregnancy and will continue to monitor your thyroid function tests every 4-6 weeks during pregnancy. If you have hypothyroidism and are taking levothyroxine, it is important to notify your doctor as soon as you know you are pregnant, so that the dose of levothyroxine can be increased accordingly to accommodate the increase in thyroid hormone replacement required during pregnancy. Because the iron and calcium in prenatal vitamins may block the absorption of thyroid hormone in your body, you should not take your prenatal vitamin within 3-4 hours of taking levothyroxine. 

American Thyroid Association. Thyroid Disease and Pregnancy. June 2012. http://www.thyroid.org/thyroid-disease-and-pregnancy/. Accessed March 13, 2014.

National Endocrine and Metabolic Diseases Information Service. Pregnancy and Thyroid Disease. April 2012. NIH Publication No. 12–6234. http://www.endocrine.niddk.nih.gov/pubs/pregnancy/. Accessed March 13, 2014.

The Endocrine Society. Executive Summary. Management of Thyroid Dysfunction in Pregnancy and Postpartum: An Endocrine Society Clinical Practice Guideline. 2012. http://www.endocrine.org/education-and-practice-management/clinical-practice-guidelines. Accessed March 13, 2014.

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