Hyperthyroidism in Pregnancy

What is hyperthyroidism?

Hyperthyroidism means overactivity of the thyroid gland, resulting in too much thyroid hormone in the bloodstream. The oversecretion of thyroid hormones leads to overactivity of the body's metabolism. Although there are several forms of hyperthyroidism, the most common is Graves' disease.

What is Graves' disease?

Graves' disease is most often associated with hyperthyroidism and is the most common cause of hyperthyroidism found in pregnancy. Researchers believe Graves' disease is caused by an antibody that stimulates the thyroid too much, in turn, causing the excess production of thyroid hormone. Graves' disease is categorized as an autoimmune disorder (a dysfunction of the body's immune system). The disease is most common in young to middle-aged women and tends to run in families.

The symptoms of Graves' disease are identical to hyperthyroidism, with the addition of three other symptoms. However, each individual may experience symptoms differently. The three additional symptoms include the following:

  • Goiter (enlarged thyroid that may cause a bulge in the neck)

  • Bulging eyes (exophthalmos)

  • Thickened skin over the shin area

What are the symptoms of hyperthyroidism?

The following are the most common symptoms of hyperthyroidism. However, each individual may experience symptoms differently. Symptoms may include:

  • Nervousness

  • Irritability

  • Increased perspiration

  • Thinning of the skin

  • Fine, brittle hair

  • Weak muscles, especially in the upper arms and thighs

  • Shaky hands

  • Fast heartbeat

  • High blood pressure

  • Increased bowel movements

  • Weight loss

  • Sleeping difficulty

  • Eye sensitivity to light

  • Staring

  • Confusion

  • Irregular menstrual cycles

The symptoms of hyperthyroidism may resemble other conditions or medical problems. Always consult your doctor for a diagnosis.

How does pregnancy affect hyperthyroidism?

Healthy thyroid glands function normally in pregnancy. Less than 1 percent of women have excessive thyroid function in pregnancy. Hyperthyroidism due to Graves disease in pregnancy tends to worsen in the first half of pregnancy, improve in the second half, and then worsen again during the postpartum period.

How does hyperthyroidism affect pregnancy?

Uncontrolled hyperthyroidism has many effects. It may lead to preterm birth (before 37 weeks of pregnancy) and low birthweight. The most common complication is preeclampsia, a form of gestational hypertension (high blood pressure of pregnancy) in women with hyperthyroidism.

A severe life-threatening form of hyperthyroidism, called thyroid storm, may complicate pregnancy. This is a condition in which there are extremely high levels of thyroid hormone that can cause high fever, dehydration, diarrhea, rapid and irregular heart rate, shock, and death, if not treated.

Medications to treat hyperthyroidism may affect the fetus and newborn. Some medications may be associated with birth defects. It is not clear if anti-thyroid medications cause hypothyroidism (low levels of thyroid) in the fetus and newborn. Neonatal hyperthyroidism may occur in a small percentage of newborns. Although most cases are temporary and do not cause problems for the baby, careful monitoring of the baby is important.

Management of hyperthyroidism during pregnancy

Specific treatment for hyperthyroidism will be determined by your doctor based on:

  • Your overall health and medical history

  • Type of hyperthyroidism

  • Extent of the disease

  • Your tolerance for specific medications, procedures, or therapies

  • Expectations for the course of the disease

  • Your opinion or preference

Treatment for hyperthyroidism is very specific for each patient. The goal of treatment is to maintain normal levels of thyroid hormone. Treatment may include:

  • Frequent monitoring of thyroid levels throughout pregnancy

  • Antithyroid medications, if the benefit of treatment outweighs the risk. Propylthiouracil and methimazole are the most common drugs used. 

  • Surgery to remove part of the thyroid (the overactive nodule)

Use of radioactive iodine, in the form of a pill or liquid, which damages thyroid cells is not safe in pregnancy.

Women with hyperthyroidism can increase their chances for a healthy pregnancy by getting early prenatal care and working with their health care providers in the management of their disease.