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Thyroid Disorders in Pregnancy

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Thyroid Disorders in Pregnancy

Definition

The thyroid is a butterfly-shaped gland located in the front of the neck. It produces hormones that control metabolism. Pregnancy hormones can affect thyroid hormones. Untreated thyroid disorders in pregnancy increase the risk of pregnancy complications. It may cause harm to the developing fetus. There are two types of thyroid disorders:
  • Hypothyroidism —the thyroid gland does not produce enough thyroid hormone
  • Hyperthyroidism —the thyroid gland produces too much thyroid hormone
The Thyroid Gland
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Causes

Hypothyroidism

Hashimoto’s disease is the most common cause of hypothyroidism. The immune system attacks the thyroid gland. Other causes of hypothyroidism in pregnancy include:
  • Inadequate treatment of pre-existing hypothyroidism
  • Overtreatment of hyperthyroidism with antithyroid medicines
  • Increased estrogen levels causes circulating thyroid hormone to become inactive

Hyperthyroidism

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, cases of high hCG can resolve on their own.

Risk Factors

Risk factors that increase your chances of developing a thyroid disorder include:

Symptoms

If you have any of these symptoms, do not assume it is due to a thyroid disorder. These symptoms may be caused by other conditions. Tell your doctor if you have any of these:
  • 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

Diagnosis

Your doctor will ask about your symptoms and medical history. A physical exam will be done. You may be referred to a doctor who specializes in hormone disorders (endocrinologist).
Your doctor may need to test your body fluids. This can be done with blood tests.
Your doctor may need to scan your thyroid to determine whether it is overactive. This can be done with a radioactive scan of the thyroid.

Treatment

Hypothyroidism

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 medicine. Levothyroxine can replace the hormone your thyroid is not producing.

Hyperthyroidism

Untreated hyperthyroidism in pregnancy is associated with:
  • Fetal tachycardia (fast heart rate)
  • Babies that are small for gestational age
  • Prematurity
  • Stillbirth
  • Fetal hyperthyroidism
  • Congenital malformations
Mild hyperthyroidism during pregnancy is often monitored closely without therapy. In some cases, you may need to take medicine. If antithyroid medicines do not work, surgical removal of your thyroid gland may be done. It is rarely recommended during pregnancy. Treatment with radioiodine destroys the thyroid gland. It is not done during pregnancy because of risk to the fetus.
Hormones associated with pregnancy can cause changes in thyroid hormone levels. Therefore, your medicine needs may vary during pregnancy. Your doctor will likely check your blood levels of thyroid hormone every 6-8 weeks during pregnancy and four weeks after your medicine dose is changed.

Prevention

There are no known guidelines to prevent thyroid disorders in pregnancy. If you think you are at risk for this disorder, talk to your doctor.

RESOURCES

The American Congress of Obstetricians and Gynecologists http://www.acog.org/For%5FPatients

American Thyroid Association http://www.thyroid.org/

CANADIAN RESOURCES

The Society of Obstetricians and Gynaecologists of Canada http://www.sogc.org

Thyroid Foundation of Canada http://www.thyroid.ca/

References

American College of Obstetricians and Gynecologists. Thyroid disease in pregnancy. Practice Bulletin No. 37. August 2002 (reaffirmed 2010).

Graves’ disease. American Thyroid Association website. Available at: http://www.thyroid.org/patients/brochures/Graves%5Fbrochure.pdf . Published 2012. Accessed December 18, 2012.

Hashimoto’s disease: what it is and how it’s treated. American Academy of Family Physicians website. Available at: http://familydoctor.org/548.xml . Updated November 2010. Accessed December 18, 2012.

Torpy J, Lynm C, Glass R. Hyperthyroidism. JAMA . 2005;294(1):146. Available at: http://jama.ama-assn.org/cgi/content/full/294/1/146 . Accessed December 18, 2012.

Revision Information

  • Reviewer: Andrea Chisholm
  • Review Date: 11/2012 -
  • Update Date: 11/26/2012 -

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

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