The Thyroid and Pregnancy

The thyroid gland is located in the middle of the lower neck. Although the thyroid gland is relatively small, it produces a hormone that influences every cell, tissue and organ in the body. The thyroid is a hormone-producing gland that regulates the body’s metabolism—the rate at which the body produces energy from nutrients and oxygen—and affects critical body functions, such as energy level and heart rate. Pregnancy has a great impact on the thyroid.

* During pregnancy, the thyroid gland produces 50 percent more thyroid hormone as compared to when a woman is not pregnant
* During pregnancy, the thyroid may increase in size by 10-15 percent.
* The normal range for thyroid function tests is different during pregnancy as compared to when a woman is not pregnant.
* The chance of developing hypothyroidism during pregnancy is increased as compared to when a woman is not pregnant.

Thyroid, mothers and babies

For the first 10 to 12 weeks of pregnancy, the baby is completely dependent on the mother for the production of the thyroid hormone

* By the end of the first trimester or pregnancy, the baby’s thyroid begins to produce the thyroid hormone.
* The baby remains dependent on the mother to ingest adequate amounts of iodine, essential for making the thyroid hormone.
* During pregnancy, adequate iodine intake is critical for the normal development of the fetal brain.
* During pregnancy, the mother must increase her intake of iodine to produce more thyroid hormone and have iodine available for the fetus
* During pregnancy the American Thyroid Association recommends that all pregnant women take a daily prenatal vitamin with 150 µg of iodine in the form of potassium iodide


Hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone, is the most common form of thyroid disease. Symptoms include fatigue, depression, forgetfulness, irregular menses and weight gain.

* Treatment for hypothyroidism during pregnancy is the same as for non-pregnant women – a synthetic form of thyroid hormone called levothyroxine.
* Prior to becoming pregnant, women on levothyroxine should see their doctor to make sure that they are on an appropriate dose.
* Women who are on levothyroxine prior to becoming pregnant typically need to increase the dose early in the first trimester by approximately 50 percent.
* Untreated, or inadequately treated, hypothyroidism is linked to spontaneous miscarriage, preterm delivery, and decreased IQ in the unborn child.
* Children born with congenital hypothyroidism (no thyroid function at birth) may have severe developmental abnormalities if not appropriately identified and treated.
* In the U.S., ALL newborns are screened for congenital hypothyroidism.
* Mandatory screening of newborns for congenital hypothyroidism and early treatment has prevented mental retardation.
* Eight percent of all women develop postpartum thyroiditis. Postpartum thyroiditis occurs in the first year after delivery and consists of hyperthyroidism followed by hypothyroidism.


Hyperthyroidism is a condition causing the gland to produce too much thyroid hormone. Symptoms include irritability, nervousness, muscle weakness, unexplained weight loss, sleep disturbances, vision problems and eye irritation.

* Hyperthyroidism may be difficult to diagnose during pregnancy because the symptoms are difficult to distinguish from normal pregnancy.
* Graves’ disease is a type of hyperthyroidism; it is an autoimmune disorder that is genetic.
* Women treated for Graves’ disease typically have their medicine decreased during pregnancy.
* Women with pre-existing Graves’ disease frequently have a flare of the disease postpartum.
* The chance of developing new onset Graves’s disease is increased during the first year postpartum.
* Inadequately treated hyperthyroidism can result in early labor and a serious complication called “pre-clampsia.”

Screening for Thyroid Disease During Pregnancy

The American Thyroid Association recommends that the following high-risk women be screened for thyroid disease either prior to becoming pregnant, or as soon as feasible once a woman becomes pregnant:

* Women with a history of thyroid disease or thyroid surgery.
* Women with a family history of thyroid disease.
* Women with a goiter.
* Women with known thyroid antibodies.
* Women with symptoms or clinical signs of hyperthyroidism or hypothyroidism.
* Women with Type I diabetes mellitus.
* Women with other autoimmune disorders.
* Women with infertility.
* Women with previous therapeutic head or neck irradiation.
* Women with a history of miscarriage or preterm delivery.

If you are interested in finding out more about thyroid disease or the American Thyroid Association, please contact us at 703.998.8890 or

The American Thyroid Association 6066 Leesburg Pike, Suite 550, Falls Church, VA 22041

Source: American Thyroid Association

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