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Hypothyroidism during Pregnancy

  • Medical Author: Ruchi Mathur, MD, FRCP(C)
  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
  • Medical Reviewer: Melissa Conrad Stöppler, MD

Hypothyroidism during pregnancy facts

  • Hypothyroidism, wherein the thyroid gland produces an inadequate amount of thyroid hormone, is a common disorder, particularly in women of childbearing age.
  • Hypothyroidism of the mother during pregnancy may result in developmental delay in the child.
  • Treatment of hypothyroidism requires thyroid hormone medication.
  • There may be indications to start thyroid hormone therapy in women who are borderline in thyroid function and who are either pregnant or desiring pregnancy.
  • The treatment goal of hypothyroidism in pregnancy is to maintain a thyroid hormone level within high normal range.
  • Pregnant women who are on thyroid hormone should have blood testing frequently during pregnancy as requirements may change.
  • Early studies found that children born to mothers with severe, untreated hypothyroidism during pregnancy had lower IQ scores and impaired psychomotor (mental and motor) development. If properly controlled, often by increasing the amount of thyroid hormone, women with hypothyroidism can have healthy, unaffected babies.

What is hypothyroidism?

  • Thyroid disease is particularly common in women of child-bearing age.
  • As a result, it is no surprise that thyroid disease may complicate the course of pregnancy.
  • Frequency varies among different populations and different countries. While pregnancy itself is a natural state and not a "disease," thyroid disorders during pregnancy affect both the mother and baby.
  • This article focuses specifically on hypothyroidism and pregnancy. After a general description of normal and abnormal thyroid function, recent data on long term consequences in children of mothers who had hypothyroidism during pregnancy will be reviewed.

What is the thyroid gland? Where is it located and what does it do?

The thyroid is a gland weighing about 15 grams (about half an ounce) that is located in the front of the neck just below the Adam's apple (cricoid cartilage). The thyroid gland is responsible for the production of the body's thyroid hormone. The thyroid responds to hormonal signals from the brain to maintain a constant level of thyroid hormone. The hormone signals are sent by specialized areas of the brain (hypothalamus and pituitary gland), eventually sending thyroid stimulating hormone (TSH) that stimulates thyroid hormone production by the thyroid gland.

Picture of the Thyroid Gland
Picture of the Thyroid Gland

What are the signs and symptoms of thyroid disease? What causes it?

Disease of the thyroid gland is extremely common. In some conditions, the thyroid may produce too much hormone. In other conditions, the thyroid may be damaged or destroyed and little, if any, thyroid hormone is produced. The main thyroid hormone is called thyroxine, or T4.

Symptoms of thyroid problems vary depending on whether there is too much or too little T4 present in the blood. With an excess of T4 (hyperthyroidism), people may complain of feeling:

Restless

  1. Emotionally hyper
  2. Hot and sweaty

Some people may have symptoms like:

  1. Tremors
  2. Trouble concentrating
  3. Weight loss
  4. Frequent bowel movements
  5. Diarrhea

If T4 levels are low (hypothyroidism) as a result of decreased production by the thyroid gland, patients often experience fatigue, lethargy, and weight gain. Constipation is common and many patients report feeling excessively cold.

How is hyperthyroidism treated during pregnancy?

In many respects, the treatment of hypothyroidism in pregnant women is similar to that in nonpregnant women.. A synthetic form of T4 is given to replace the missing hormone. The medication dose is regularly adjusted to maintain a steady blood level of thyroid hormone within the normal range, and the requirments for this hormone may increase during pregnancy. Therefore, it is routine practice to monitor the blood level of the thyroid stimulating hormone (TSH) during pregnancy. For more information, please read the article on Hypothyroidism.

Does hypothyroidism during pregnancy hurt the fetus?

Doctors have known for years of a link between mothers with untreated severe hypothyroidism during pregnancy and developmental delay in their children after birth. This was particularly seen in mothers who came from iodine deficient areas of the country (iodine is necessary to produce thyroid hormone and is now a common component of the salt in our foods), and was observed in mothers with autoimmune thyroid disease, such as Hashimoto's thyroiditis. Some studies have suggested that mild untreated hypothyroidism may also affect the baby’s brain development, but this relationship is less clear.

How can you avoid the complications of hypothyroidism in pregnancy?

A number of medical associations and organizations have made recommendations on screening for thyroid disease. Some of the recommendations are:

  • All women who are planning a pregnancy should be considered for screening of thyroid disease.
  • All pregnant women with a goiter (enlarged thyroid), high blood levels of thyroid antibodies, a family history of thyroid disease, or symptoms of hypothyroidism should be tested for hypothyroidism.
  • In women who are borderline, or sub-clinical, hypothyroid (for example, not in the laboratory range for true hypothyroidism, but within the low normal range) and who also have positive antibodies (which may indicate an ongoing autoimmune thyroid destruction), therapy with low dose thyroid hormone at the onset of pregnancy may be beneficial.
  • There is some evidence that the antibodies that may contribute to hypothyroidism can play a role in pregnancy. Some data suggest that selenium supplementation may be of benefit in women with high antibody levels at the time of preconception. This should be reviewed with your doctor.
  • Women who are on thyroid hormone replacement before pregnancy should also be tested to make certain that their levels are appropriate. During pregnancy, the medication dose required may increase by up to 50%. Increases may be required as early as in the first trimester.
  • Dosing is dynamic during pregnancy and should be closely monitored by regular blood testing. As the pregnancy progresses, many women require higher doses of hormone replacement.
  • The dosage of thyroid hormone replacement during and after pregnancy should be carefully monitored using the blood thyroid stimulating hormone (TSH) value. The laboratory ranges for normal TSH are quite wide
  • In women with hypothyroidism before conception, most go back to their pre-pregnancy dose of thyroid hormone within a few weeks to months after delivery.

The management of each woman's situation is considered individually after consultation with her physician. The benefits of treatment extend not only to pregnant women with hypothyroidism, but also to their children.

How early does the mother's thyroid hormone affect the unborn baby?

Before birth a baby is entirely dependent on the mother for thyroid hormone until the baby's own thyroid gland can start to function. This usually does not occur until about 12 weeks of gestation (the end of the first trimester of pregnancy). Thus, hypothyroidism of the mother may play a role early on, before many women realize they are pregnant! In fact, the babies of mothers who were hypothyroid in the first part of pregnancy, then adequately treated, exhibited slower motor development than the babies of normal mothers. However, during the latter part of pregnancy, severe, untreated hypothyroidism in the mother can also have adverse effects on the baby, as pointed out by the research described above. These children are more likely to have intellectual impairment.

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Reviewed on 11/19/2018

REFERENCE:

Ross, DS, MD, et al. "Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment" UpToDate. Updated: May 14, 2019.
<https://www.uptodate.com/contents/hypothyroidism-during-pregnancy-clinical-manifestations-diagnosis-and-treatment>

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