Note: The Pregistry website includes expert reports on more than 2000 medications, 300 diseases, and 150 common exposures during pregnancy and lactation. For the topic Thyroid Disease, go here. For the topic Hyperthyroidism, go here. These expert reports are free of charge and can be saved and shared.
There are three common thyroid diseases that can occur during pregnancy. They can be caused by the way pregnancy affects your immune system. As long as they are recognized and treated, they should not affect your pregnancy or your baby. However, if left untreated, they could be a problem for both pregnancy and baby. The three diseases are Graves’ disease, Hashimoto’s disease, and postpartum thyroiditis.
Some Thyroid Basics
Your thyroid gland is a butterfly-shaped gland in the front of your neck. It makes important chemical messengers, called thyroid hormones, that control how your body uses energy. The pregnancy hormones, hCG and estrogen, both have stimulating effects on the thyroid. In fact, in normal pregnancy your thyroid hormones may increase slightly, and your thyroid may increase in size by about 10 percent, although this is usually not noticeable.
Many women have mild symptoms due to pregnancy stimulation of the thyroid. These can include a rapid heartbeat, feeling hot, or feeling tired. There is a good reason for your thyroid to get more active. Your baby needs your thyroid hormones for normal development of her or his brain and nervous system. During the first 12 weeks of pregnancy, your baby is completely dependent on you for thyroid hormones. By 18 to 20 weeks, your baby’s thyroid will be developed enough to makes its own hormones.
Although the exact cause of thyroid disease during pregnancy is not known, it may be that the stimulation of the thyroid triggers an abnormal immune system reaction in some women. This reaction is called autoimmune disease. Normally, your immune system makes antibodies to attack foreign invaders like germs. When you have autoimmune disease in pregnancy, your immune system antibodies may attack your thyroid.
What Happens in Graves’ Disease?
In Graves’ disease, your immune system makes an antibody called thyroid stimulating immunoglobulin (TSI). TSI makes your thyroid overactive, a condition called hyperthyroidism. Graves’ disease occurs in about 1 in 1,000 pregnancies. You can also have Graves’ disease before pregnancy.
Signs and symptoms of hyperthyroid disease include:
- Heart palpitations
- Weight loss or failure to gain weight during pregnancy
- Severe morning sickness
If you develop symptoms of hyperthyroidism during pregnancy, your doctor can do blood tests to look for abnormal levels of thyroid hormones and the TSI antibody. Your doctor will do frequent testing if you have been diagnosed with Graves’ disease before pregnancy. Graves’ disease may get worse early in pregnancy, get better later in pregnancy, and then flare again after pregnancy.
If your symptoms are mild, you may not need treatment, but your doctor will continue to do frequent blood checks. Severe or untreated hyperthyroidism can increase your risk for miscarriage, premature birth, or low birth weight baby. It can cause you to have dangerous high blood pressure and heart failure. Your baby may also have high blood pressure or heart failure.
If your doctor thinks you or your baby are at risk, you may be treated with an antithyroid medication that decreases levels of thyroid hormone. Some people are allergic to this medication or have severe side effects. In these cases, surgery can be done during pregnancy to remove the thyroid gland. This is a last resort that is rarely needed.
Although the exact cause of thyroid disease during pregnancy is not known, it may be that the stimulation of the thyroid triggers an abnormal immune system reaction in some women.
What Happens in Hashimoto’s Disease?
In Hashimoto’s disease your immune system makes antibodies called anti-thyroid antibodies. These antibodies make your thyroid underactive, a condition called hypothyroidism. Hashimoto’s disease is more common than Graves’ disease. It occurs in about 3 in 100 pregnancies. You can also have Hashimoto’s disease without being pregnant.
Signs and symptoms of hypothyroid disease include:
- Feeling cold
- Muscle aches or cramps
- Dry skin
- Poor concentration
If you develop symptoms of hypothyroidism during pregnancy, your doctor can do blood tests to look for low levels of thyroid hormone and anti-thyroid antibodies. Your doctor will do frequent testing if you have been diagnosed with Hashimoto’s disease before pregnancy. Because your baby depends on your thyroid hormones for brain and nervous system development, untreated hypothyroidism, especially early in pregnancy, may affect your baby’s brain development.
If your symptoms are mild, you may not need treatment, but your doctor will continue to do frequent blood checks. Severe or untreated hypothyroidism can increase your risk for anemia, miscarriage, stillbirth, premature birth, or a low birth weight baby.
If your doctor thinks you or your baby are at risk, you may be treated with a thyroid hormone replacement medication. This medication works well and is safe for your baby. If you were diagnosed with Hashimoto’s disease before pregnancy and you are already on thyroid replacement, your doctor may increase your dose early in pregnancy to protect your baby.
What Happens in Postpartum Thyroiditis?
This is the only thyroid disease that happens after birth. This disease is very similar to Hashimoto’s disease. It occurs in between 5 to 10 percent of pregnancies. Your autoimmune system makes antibodies that attack your thyroid and cause inflammation. At first – during the first three postpartum months – the inflammation causes thyroid hormone to leak out of your thyroid gland, causing hyperthyroidism. Over time – up to one year or longer – inflammation may cause hypothyroidism. In about 20 percent of women, the hypothyroidism may be long lasting.
You may be at higher risk for postpartum thyroiditis if you have Type 1 diabetes, have anti-thyroid antibodies, or you have had this condition during an earlier pregnancy. Some women only have the hyperthyroid phase, some only have hypothyroid, and some have both. The hyperthyroid phase does not require antithyroid medication. Your doctor may treat you with a milder medication called a beta-blocker.
If you have hypothyroidism, you may be treated with thyroid hormone replacement. Neither hyper or hypo postpartum thyroiditis should keep you from being able to breastfeed your baby. Both thyroid hormone replacement and beta-blockers can be used during breastfeeding.
Prevention of Hypothyroidism During Pregnancy
There is no known way to prevent autoimmune thyroid disease during pregnancy. However, you can prevent hypothyroidism caused by iodine deficiency. Both you and your baby need iodine to make thyroid hormones. Babies who do not get enough iodine in early pregnancy may be at risk for poor brain and nervous system development.
Most women get enough iodine from foods, and this iodine is enough for a baby’s thyroid gland to develop normally. However, some foods highest in iodine, like fish and iodized salt, are avoided by women during pregnancy to prevent high blood pressure and fluid retention (salt) or mercury poisoning (fish).
Other foods that are high in iodine include eggs, meat, and poultry. You should make sure you have enough iodine in your prenatal vitamins. The recommended dose is somewhere between 150 and 200 micrograms. Many doctors now routinely check iodine levels in pregnant women.
Thyroid diseases can be safely managed during pregnancy. The risk comes from missing the diagnosis and letting a disease go untreated. Ask your doctor if you should have your iodine checked before pregnancy or early in pregnancy. Let your doctor know if you have any history of hyper or hypothyroidism before pregnancy or as soon as you find out you are pregnant. Let your doctor know if you have any symptoms of hyper or hypothyroidism during your pregnancy.