The thyroid is a butterfly-shaped gland located in the front of the neck. It produces hormones that control metabolism. Thyroid disorders in pregnancy can be a particular concern because pregnancy-related hormones can affect thyroid hormones. Untreated thyroid disorders in pregnancy increase the risk of pregnancy complications. It may cause harm to the developing fetus.

Hypothyroidism is a disease in which the thyroid gland does not produce enough thyroid hormone.

Hyperthyroidism is a disease in which the thyroid gland produces too much thyroid hormone.

The Thyroid Gland

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Hashimoto’s disease is the most common cause of hypothyroidism . The immune system attacks the thyroid gland. Other causes of hypothyroidism in pregnancy include the following:

  • Inadequate treatment of pre-existing hypothyroidism
  • Overtreatment of hyperthyroidism with antithyroid medications
  • Increased estrogen levels (causes circulating thyroid hormone to become inactive)


Graves’ disease is characterized by overactivity of the thyroid. It is the most common cause of hyperthyroidism . Another cause of hyperthyroidism in pregnancy is very high levels of human chorionic gonadotropin (hCG). However, such cases usually resolve spontaneously.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

The following factors increase your chance of having thyroid disorders in pregnancy. If you have any of these risk factors, tell your doctor:

  • Personal or family history of a thyroid disorder
  • History of treatment for a thyroid disorder
  • Presence of a goiter (enlarged thyroid gland)
  • Hyperemesis gravidarum (severe forms of morning sickness)
  • Prematurely gray hair
  • Family or personal history of immune problems (eg, type 1 diabetes , vitiligo )


If you experience any of these symptoms during pregnancy, do not assume it is due to a thyroid disorder. These symptoms may be caused by other, less serious health conditions. Many people with thyroid disorders have no symptoms at all. If you experience any one of them, see your physician.

Symptoms of Hypothyroidism

  • Goiter (swelling) in the front of your neck
  • A feeling of fullness or tightness in your throat
  • Trouble swallowing foods or liquids
  • Tiredness
  • Forgetfulness
  • Depression
  • Dry skin
  • Slow heartbeat
  • Weight gain
  • Constipation
  • Intolerance to cold

Symptoms of Hyperthyroidism

  • Unexplained weight loss
  • Heart palpitations or abnormal heart rhythm
  • Sweating
  • Nervousness
  • Tremors
  • Protruding eyes
  • Intolerance to heat


Your doctor will ask about your symptoms and medical history, and perform a physical exam. You may be referred to a doctor who specializes in hormone disorders (endocrinologist).

Tests may include the following:

  • Blood tests—to measure thyroid-stimulating hormone (TSH), thyroid hormones (thyroxine, or T4, and triiodothyronine, or T3), and to look for the presence of antibodies that attack the thyroid gland
  • Radioactive scan of the thyroid—to determine whether the thyroid is overactive (this is usually avoided during pregnancy, though, due to risks to the developing fetus)



Untreated hypothyroidism in pregnancy can:

  • Increase the risk of miscarriage and fetal death
  • Negatively impact the child’s psychological development, IQ score, motor skills, attention, language, and reading abilities

To treat hypothyroidism, your doctor will prescribe an oral medication. Levothyroxine (Synthroid) can replace the hormone your thyroid is not producing.


Untreated hyperthyroidism in pregnancy is associated with:

  • Fetal tachycardia (fast heart rate)
  • Babies that are small for gestational age
  • Prematurity
  • Stillbirths
  • Fetal hyperthyroidism
  • Congenital malformations

To decrease the risk of hypothyroidism, mild hyperthyroidism during pregnancy is often monitored closely without therapy. Antithyroid drug therapy ( methimazole , propylthiouracil ) is used to treat more severe hyperthyroidism. Propylthiouracil is usually chosen, since it may not pass over the placenta as much. Medicine that passes over the placenta can effect the developing fetus.

If antithyroid medications do not work, surgical removal of your thyroid gland may be performed. It is very rarely recommended during pregnancy. Treatment with radioiodine that destroys the thyroid gland, is contraindicated during pregnancy because of risk to the fetus.

Hormones associated with pregnancy can cause changes in thyroid hormone levels. Therefore, your medication needs may fluctuate widely during pregnancy. Your doctor will likely check your blood levels of thyroid hormone every 6-8 weeks during pregnancy, and four weeks after your medication dose is changed.


There are no known guidelines for preventing thyroid disorders in pregnancy. However, if you think you are at risk for this disease, talk to your doctor about setting up an appropriate schedule of check-ups.