Thyroid Problems and Pregnancy

The most common thyroid disorder occurring around or during pregnancy is thyroid hormone deficiency, or hypothyroidism. The details of hypothyroidism are covered on several other pages on our site, so only those factors pertaining to pregnancy are discussed here. Hypothyroidism can cause a variety of changes in a woman's menstrual periods: irregularity, heavy periods, or loss of periods. When hypothyroidism is severe, it can reduce a woman's chances of becoming pregnant. Checking thyroid gland function with a simple blood test is an important part of evaluating a woman who has trouble becoming pregnant. If detected, an underactive thyroid gland can be easily treated with thyroid hormone replacement therapy. If thyroid blood tests are normal, however, treating an infertile woman with thyroid hormones will not help at all, and may cause other problems.

Because some of the symptoms of hypothyroidism such as tiredness and weight gain are already quite common in pregnant women, it is often overlooked and not considered as a possible cause of these symptoms. Blood tests, particularly measuring the TSH level, can determine whether a pregnant woman's problems are due to hypothyroidism or not.

Since thyroid medications (particularly Levothyroxine) are essentially identical to the thyroid hormone made by the normal thyroid gland, a woman with an underactive thyroid gland can feel confident that it is perfectly safe to take thyroid hormone medication during pregnancy. There are no side effects for the mother or the baby as long as the proper dose is used. In the case where hypothyroidism in the mother is NOT detected, the thyroid will still develop normally in the baby.

Women with previously treated hypothyroidism should be aware that their dose of medication may have to be increased during pregnancy. They should contact their doctor, who should check their blood level of TSH periodically throughout pregnancy to see if their medication dose needs adjustment. Thyroid function tests should continue to be reviewed every 2-3 months throughout the pregnancy. After delivery, the thyroxine dose should be returned to the pre-pregnancy dose and thyroid function tests reviewed two months later.

Hyperthyroidism and Pregnancy

Hyperthyroidism refers to the signs and symptoms which are due to the production of too much thyroid hormone. [Hyperthyroidism is covered in great deal on other pages on this site (about 8 in all), so only that part of hyperthyroidism which pertains to the pregnant mother will be discussed here]. An overactive thyroid gland (hyperthyroidism) often has its onset in younger women. Because a woman may think that feeling warm, having a hard or fast heartbeats, nervousness, trouble sleeping, or nausea with weight loss are just parts of being pregnant, the symptoms and signs of this condition may be overlooked during pregnancy.

In women who are not pregnant, hyperthyroidism can affect menstrual periods, making them irregular, lighter, or disappear altogether. It may be harder for hyperthyroid women to become pregnant, and they are more likely to have miscarriages. If a woman with infertility or repeated miscarriages has symptoms of hyperthyroidism, it is important to rule out this condition with thyroid blood tests. It is very important that hyperthyroidism be controlled in pregnant women since the risks of miscarriage or birth defects are much higher without therapy. Fortunately, there are effective treatments available. Antithyroid medications cut down the thyroid gland's overproduction of hormones and are reviewed on another page on this site. When taken faithfully, they control hyperthyroidism within a few weeks. In pregnant women thyroid experts consider propylthiouracil (PTU) the safest drug. Because PTU can also affect the baby's thyroid gland, it is very important that pregnant women be monitored closely with examinations and blood tests so that the PTU dose can be adjusted. In rare cases when a pregnant woman cannot take PTU for some reason (allergy or other side effects), surgery to remove the thyroid gland is the only alternative and should be undertaken prior to or even during the pregnancy if necessary. Although radioactive iodine is a very effective treatment for other patients with hyperthyroidism, it should never be given during pregnancy because the baby's thyroid gland could be damaged.

Because treating hyperthyroidism during pregnancy can be a bit tricky, it is usually best for women who plan to have children in the near future to have their thyroid condition permanently cured. Antithyroid medications alone may not be the best approach in these cases because hyperthyroidism often returns when medications is stopped. Radioactive iodine is the most widely recommended permanent treatment with surgical removal being the second (but widely used) choice. It is concentrated by thyroid cells and damages them with little radiation to the rest of the body. This is why it cannot be given to a pregnant woman, since the radioactive iodine could cross the placenta and destroy normal thyroid cells in the baby. The only common side effect of radioactive iodine treatment is underactivity of the thyroid gland, which occurs because too many thyroid cells were destroyed. This can be easily and safely treated with levothyroxine. There is no evidence that radioactive iodine treatment of hyperthyroidism interferes with a woman's future chances of becoming pregnant and delivering a healthy baby. For more information on the treatment options of hyperthyroidism see our page on this topic.

Thyroid Problems After Pregnancy

One of every twenty women develop thyroid inflammation within a few months after delivery of their baby, a condition called postpartum thyroiditis. This form of thyroid inflammation is painless and causes little or no gland enlargement. However, the condition interferes with the gland's production of thyroid hormones. Thyroid hormone may leak out of the inflamed gland in large amounts, causing hyperthyroidism that lasts for several weeks. Later on, the injured gland may not be able to make enough thyroid hormone, resulting in temporary hypothyroidism. Symptoms of hyperthyroidism and hypothyroidism may not be recognized when they occur in a new mother. They may be simply attributed to lack of sleep, nervousness, or depression.

Thyroid Symptoms Occasionally Overlooked in New Mothers

Hyperthyroidism

• Fatigue
• Insomnia
• Nervousness
• Irritability

Hypothyroidism

• Fatigue
• Depression
• Easily upset
• Trouble losing weight

Postpartum thyroiditis goes away on its own after one to four months. While it is active, however, women often benefit from treatment for their thyroid hormone excess or deficiency. Some of the symptoms caused by too much thyroid hormone, such as tremor or palpitations, can be improved promptly by medications called beta-blockers(e.g., propranolol). Antithyroid drugs, radioactive iodine, and surgery do not need to be considered because this form of hyperthyroidism is only temporary. If thyroid hormone deficiency develops, it can be treated for one to six months with levothyroxine. Women who have had an episode of postpartum thyroiditis are very likely to develop the problem again after future pregnancies. Although each episode usually resolves completely, one out of four women with postpartum thyroiditis goes on to develop a permanently underactive thyroid gland in future. Of course, levothyroxine fully corrects their thyroid hormone deficiency, and when used in the correct dose, can be safely taken without side effects or complications.

Thyroid Problems in the Baby

Rarely, a baby may be born without a thyroid gland. This birth defect is not caused by thyroid problems in the mother. If an infant's hypothyroidism is not recognized and treated promptly, he/she will not develop normally. Therefore, all newborn babies in the United States routinely have a blood test to be sure that hypothyroidism is diagnosed and treated. Most thyroid medications will have no effect on the baby. The exception to this generality is the administration of radioactive iodine to the mother during pregnancy. Radioactive iodine can cross the placenta and it can destroy thyroid cells in the fetus.

More about Hypothyroidism

More about Hyperthyroidism

Return to Thyroid Overview

Much of this information was obtained from a patient information pamphlet produced and distributed by the American Thyroid Association. Their expertise is acknowledged and appreciated.