Autoimmune Thyroid Disease and Pregnancy 

  • Author: Dotun A Ogunyemi, MD; Chief Editor: Carl V Smith, MD   more...
 
Updated: Mar 8, 2012
 

Background

Thyroid disorders are the second most common endocrinologic disorders found in pregnancy. Overt hypothyroidism is estimated to occur in 0.3-0.5% of pregnancies. Subclinical hypothyroidism appears to occur in 2-3%, and hyperthyroidism is present in 0.1-0.4%.[1]

Autoimmune thyroid dysfunctions remain a common cause of both hyperthyroidism and hypothyroidism in pregnant women. Graves disease accounts for more than 85% of all cases of hyperthyroid, whereas Hashimoto thyroiditis is the most common cause of hypothyroidism.

Postpartum thyroiditis (PPT) reportedly affects 4-10% of women. PPT is an autoimmune thyroid disease that occurs during the first year after delivery. Women with PPT present with transient thyrotoxicosis, hypothyroidism, or transient thyrotoxicosis followed by hypothyroidism. This presentation may be unrecognized, but is important because it predisposes the woman to develop permanent hypothyroidism.

Of interest, symptoms of autoimmune thyroid diseases tend to improve during pregnancy. A postpartum exacerbation is not uncommon and perhaps occurs because of an alteration in the maternal immune system during pregnancy. The improvement in thyroid autoimmune diseases is thought to be due to the altered immune status in pregnancy.

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Pathophysiology

The defect that predisposes an individual to develop autoimmune thyroid disease is still unknown. Proposed mechanisms include a tissue-specific defect in suppressor T-cell activity, a genetically programmed presentation of a thyroid-specific antigen, and an idiotype/anti-idiotype reaction. Regardless of the cause, the common outcome is the production of 1 or more types of autoantibodies. A study by Thangaratinam concluded that the presence of maternal thyroid autoantibodies in women with normal thyroid function is strongly associated with serious conditions, including preterm delivery and miscarriage.[2]

Graves disease

Adams and Purves described the concept of Graves disease as an autoimmune dysfunction of the thyroid gland. These investigators noted that the sera of patients with Graves disease contained a factor that stimulated the murine thyroid gland. This factor had a longer duration of action than that of thyrotropin (ie, thyroid-stimulating hormone [TSH]), the long-acting thyroid stimulator.[3, 4, 5, 6]

Further studies revealed that these long-acting thyroid stimulators are autoantibodies directed against the TSH receptor. The activating versions of the TSH receptor are the thyroid-stimulating autoantibodies, which activate adenylate cyclase and which stimulate thyroid function.

In terms of histologic features, the thyroid glands of patients with Graves disease show follicular hypertrophy and hyperplasia (see Histologic Findings).

Hashimoto thyroiditis

Hashimoto thyroiditis is also known as goitrous chronic thyroiditis. Almost all patients with this disease have positive test results for the thyroid peroxidase antibody (anti-TPO), an autoantibody against thyroid peroxidase enzyme. Of these patients, 50-70% also have positive results for antithyroglobulin antibodies.

Classic histologic findings of Hashimoto thyroiditis are extensive lymphocytic infiltration, follicular rupture, eosinophilia, various degrees of hyperplasia, and fibrosis (see Histologic Findings).

Atrophic chronic thyroiditis

Atrophic chronic thyroiditis is a rare autoimmune cause of hypothyroidism. This condition is characterized by the presence of blocking autoantibodies to the TSH receptors.

Postpartum thyroiditis

PPT is a variant of chronic autoimmune thyroiditis (Hashimoto thyroiditis). PTT is characterized by the presence of antimicrosomal antibodies. Histologic examination of PTT-affected thyroid glands affected reveals destructive lymphocytic thyroiditis (see Histologic Findings).

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Epidemiology

Frequency

United States

Hyperthyroidism affects 0.1-0.4% of pregnancies. Graves disease accounts for 85% of these cases. Hypothyroidism affects up to 2.2% of pregnant women and Hashimoto thyroiditis is the most common cause. Atrophic thyroiditis is less common. Postpartum thyroiditis has a prevalence ranging from 3.3-8.8% in the United States.[1]

International

The reported range for the frequency of PPT is wide. In Thailand, as few as 2 in 100 postpartum women are affected. By comparison, some Canadian studies revealed a frequency of 2 per 10 postpartum women. These differences may be due to variations in diagnostic criteria, in genetic factors, and in iodine consumption.

Mortality/Morbidity

Fetal and maternal outcomes improve when thyroid function returns to normal.

Hyperthyroidism

Uncontrolled hyperthyroidism, especially in the second half of pregnancy, can lead to numerous complications. Maternal complications include miscarriage, infection, preeclampsia, preterm delivery, congestive heart failure (CHF), thyroid storm, and placental abruption. Fetal and neonatal complications include prematurity, small size for gestational age, intrauterine fetal death, and fetal or neonatal goiter and/or thyrotoxicosis. Overtreatment may cause iatrogenic fetal hypothyroidism.

Hypothyroidism

Maternal complications of untreated hypothyroidism include microcytic anemia, preeclampsia, placental abruption, postpartum hemorrhage, cardiac dysfunction, and miscarriage. Fetal or neonatal complications include prematurity, low birth weight, congenital anomalies, stillbirth, and poor neuropsychological development.

In particular, overt maternal hypothyroidism is associated with neonatal neurologic developmental delay because of the transplacental transfer of thyroid hormone in early pregnancy is inadequate. This process is required for brain development. The fetal thyroid does not begin to concentrate iodine until 10-12 weeks of gestation. Therefore, before this time, the mother must provide for all of the fetus' thyroxine (T4) requirements.

Approximately 10-15% of the population has thyroid antibodies. These antibodies have been linked to an increased risk of spontaneous abortion.

Subclinical hypothyroidism also has been associated with spontaneous abortion and with preterm labor.

A study by Wilson et al found that women diagnosed with subclinical hypothyroidism during their pregnancy have an increased risk for severe preeclampsia.[7]

Postpartum thyroiditis

Complications associated with PPT are maternal, and depression is common. Permanent hypothyroidism occurs in as many as 30% of women. These patients are also at high risk for recurrent PPT with subsequent pregnancies.

Sex

Autoimmune thyroid diseases occur more often in women than in men. The female-to-male ratio is 5-10:1.[8]

Age

Autoimmune thyroid dysfunction most often affects women of reproductive age.

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Contributor Information and Disclosures
Author

Dotun A Ogunyemi, MD  Associate Professor of Obstetrics and Gynecology, David Geffen School of Medicine at UCLA; Residency Program Director, Clerkship Director, Department of Obstetrics and Gynecology, Cedars Sinai Medical Center

Dotun A Ogunyemi, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, American Medical Association, National Medical Association, and Society for Maternal-Fetal Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Carl V Smith, MD  The Distinguished Chris J and Marie A Olson Chair of Obstetrics and Gynecology, Professor, Department of Obstetrics and Gynecology, Senior Associate Dean for Clinical Affairs, University of Nebraska Medical Center

Carl V Smith, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Council of University Chairs of Obstetrics and Gynecology, Nebraska Medical Association, and Society for Maternal-Fetal Medicine

Disclosure: Nothing to disclose.

Frederick B Gaupp, MD  Consulting Staff, Department of Family Practice, Hancock Medical Center

Frederick B Gaupp, MD is a member of the following medical societies: American Academy of Family Physicians

Disclosure: Nothing to disclose.

Chief Editor

Carl V Smith, MD  The Distinguished Chris J and Marie A Olson Chair of Obstetrics and Gynecology, Professor, Department of Obstetrics and Gynecology, Senior Associate Dean for Clinical Affairs, University of Nebraska Medical Center

Carl V Smith, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Council of University Chairs of Obstetrics and Gynecology, Nebraska Medical Association, and Society for Maternal-Fetal Medicine

Disclosure: Nothing to disclose.

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Table. Mean Increases in Dosages of Thyroid Hormone According to Serum TSH levels
Serum TSH level,



mIU/mL or mIU/L



Increase,



mcg/d



5-1025-50
10-2050-75
< 2075-100
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