Thyroid conditions during pregnancy

What is the thyroid?

The thyroid is a tiny, butterfly-shaped gland in your neck. A gland is an organ that makes substances that help your body work. The thyroid makes hormones (chemicals) that play a big role in your health. For example, thyroid hormones can affect your heart rate (how fast your heart beats) and your metabolism (how well and fast your body processes what you eat and drink).

Sometimes the thyroid gland makes too much or too little of certain hormones. When this happens, you have a thyroid disorder. Some women have a thyroid disorder that begins before pregnancy (also called a pre-existing condition). Others may develop thyroid problems for the first time during pregnancy or soon after giving birth.

With treatment, a thyroid condition may not cause any problems during pregnancy. But untreated thyroid conditions can cause problems for you and your baby during pregnancy and after birth.

What are the main kinds of thyroid conditions?

There are two main kinds of thyroid conditions:

1. Hyperthyroidism (“hyper” means too much). This is when the thyroid is overactive and makes too much thyroid hormone. This condition can cause many of your body’s functions to speed up. Hyperthyroidism during pregnancy usually is caused by an autoimmune disorder called Graves’ disease. Autoimmune disorders are health conditions that happen when antibodies (cells in the body that fight off infections) attack healthy tissue by mistake. If you have Graves’ disease, your immune system makes antibodies that cause your thyroid to make too much thyroid hormone. In rare cases, hyperthyroidism is linked to a severe form of morning sickness called hyperemesis gravidarum (excessive nausea and vomiting during pregnancy). Also in rare cases, hyperthyroidism can be caused by thyroid nodules. These are lumps in your thyroid that make too much thyroid hormone.
2. Hypothyroidism (“hypo” means too little or not enough). This is when the thyroid is underactive and doesn’t make enough thyroid hormones, so many of your body’s functions slow down. Hypothyroidism during pregnancy usually is caused by an autoimmune disorder called Hashimoto’s disease. When you have Hashimoto’s disease, your immune system makes antibodies that attack your thyroid and damage it so it can’t produce thyroid hormones.

If you have a thyroid condition during pregnancy, treatment can help you have a healthy pregnancy and a healthy baby.

How are thyroid conditions during pregnancy diagnosed?

Health care providers don’t usually test your thyroid before or during pregnancy unless you’re at high risk of having a thyroid condition or you have signs or symptoms of one. If you have signs or symptoms of a thyroid condition, especially during pregnancy, tell your provider. Signs of a condition are things someone else can see or know about you, like that you have a rash or you’re coughing. Symptoms are things you feel yourself that others can’t see, like having a sore throat or feeling dizzy. Signs and symptoms of thyroid conditions may appear slowly over time. Many are signs and symptoms of other health conditions, so having one doesn’t always mean you have a thyroid problem.

Your provider gives you a physical exam and a blood test to check for thyroid conditions. The blood test measures the levels of thyroid hormones and thyroid stimulating hormone (also called TSH) in your body. TSH is a hormone that tells your thyroid gland to make thyroid hormones. If you think you may have a thyroid condition, ask your provider about testing.

Are you at risk for having a thyroid condition during pregnancy?

You’re at higher risk for a thyroid condition during pregnancy than other women if you:

• Are currently being treated for a thyroid condition or you have thyroid nodules or a goiter. A goiter is a swollen thyroid gland that can make your neck look swollen.
• Have had a thyroid condition in the past (including after giving birth), or you’ve had a baby who had a thyroid condition
• Have an autoimmune disorder or you have a family history of autoimmune thyroid disease, like Graves’ disease or Hashimoto’s disease. Family history means that the condition runs in your family (people in your family have or have had the condition). Use the March of Dimes family health history form and share it with your provider. The form helps you keep a record of any health conditions and treatments that you, your partner and everyone in both of your families has had. It can help your provider check for health conditions that may affect your pregnancy. If you have a family history of thyroid or autoimmune conditions, ask your provider about testing.
• Have type 1 diabetes. Diabetes is a condition in which your body has too much sugar (called glucose) in the blood. Type 1 diabetes is a kind of preexisting diabetes, which means you have it before you get pregnant. If you have type 1 diabetes, your pancreas stops making insulin. Insulin is a hormone that helps keep the right amount of glucose in your body.
• Have had high-dose neck radiation or treatment for hyperthyroidism. Radiation is a kind of energy. It travels as rays or particles in the air.

If you’ve had a thyroid condition or think you’re at risk for having a thyroid condition, ask your provider about testing.

What are signs and symptoms of hyperthyroidism?

Hyperthyroidism that’s untreated or not treated correctly is linked to problems for women and babies during pregnancy and after birth.

Problems for women can include:

• Preeclampsia. This is a serious blood pressure condition that can happen after the 20th week of pregnancy or after giving birth (also called postpartum preeclampsia). It’s when a woman has high blood pressure and signs that some of her organs, like her kidneys and liver, may not be working normally. Blood pressure is the force of blood that pushes against the walls of your arteries. Arteries are blood vessels that carry blood away from your heart to other parts of the body. High blood pressure (also called hypertension) is when the force of blood against the walls of the blood vessels is too high. It can stress your heart and cause problems during pregnancy.
• Pulmonary hypertension. This is a kind of high blood pressure that happens in the arteries in your lungs and on the right side of your heart.
• Placental abruption. This is a serious condition in which the placenta separates from the wall of the uterus before birth. The placenta grows in your uterus (womb) and supplies the baby with food and oxygen through the umbilical cord.
• Heart failure. This is when your heart can’t pump enough blood to the rest of your body.
• Thyroid storm. This is when your symptoms suddenly get much worse. It’s a rare, but life-threatening condition during pregnancy. Pregnant women who have thyroid storm are at high risk of heart failure.

Problems for babies can include:

• Preterm birth. This is birth that happen too early, before 37 weeks of pregnancy.
• Goiter
• Low birthweight. This is when a baby is born weighing less than 5 pounds, 8 ounces.
• Thyroid problems. Antibodies that cause Graves’ disease cross the placenta during pregnancy. If you have Graves’ disease during pregnancy, your baby is at risk for thyroid conditions during and after birth. If you had treatment for Graves’ disease with radioactive iodine before pregnancy, your baby is at risk for Graves’ disease.
• Miscarriage or stillbirth. Miscarriage is when a baby dies in the womb before 20 weeks of pregnancy. Stillbirth is when a baby dies in the womb after 20 weeks of pregnancy.

How can hypothyroidism affect pregnancy?

Untreated hypothyroidism during pregnancy is linked to problems for women and babies during pregnancy and after birth.

Problems for women can include:  

• Anemia. This is when you don’t have enough healthy red blood cells to carry oxygen to the rest of your body.
• Gestational hypertension. This is high blood pressure that starts after 20 weeks of pregnancy and goes away after you give birth.
• Preeclampsia
• Placental abruption
• Postpartum hemorrhage (also called PPH). This when a woman has heavy bleeding after giving birth. It’s a serious but rare condition. It usually happens within 1 day of giving birth, but it can happen up to 12 weeks after having a baby.
• Myxedema, a rare condition caused by severe, untreated hypothyroidism that can cause you to go into a coma and can cause death
• Heart failure. This is when your heart doesn’t pump blood as well as it should. Heart failure cause by hypothyroidism is rare.

Problems for babies can include:

• Infantile myxedema, a condition that’s linked to severe hypothyroidism. It can cause dwarfism, intellectual disabilities and other problems. Dwarfism (also called little people) is a condition in which a person is very short (less than 4 feet 10 inches as an adult). Intellectual disability causes a lower-than-average intelligence and a lack of skills needed to function in daily life.
• Low birthweight.
• Problems with growth and brain and nervous system development. The nervous system is made up of your brain, spinal cord and nerves. Your nervous system helps you move, think and feel. Untreated hypothyroidism, especially when it happens during the first trimester, can cause low IQ in a baby.
• Thyroid problems. This is rare, but it can happen in babies of women with Hashimoto’s disease because the antibodies can cross the placenta during pregnancy.
• Miscarriage or stillbirth

What is postpartum thyroiditis?

In about 1 to 21 in 100 women (1 to 21 percent), the thyroid becomes swollen in the first year after giving birth. This is an autoimmune condition called postpartum thyroiditis. It can cause your thyroid to be overactive, underactive and even a combination of both.

How are thyroid conditions treated during pregnancy and while breastfeeding?

Many medicines used to treat thyroid conditions during pregnancy are safe for your baby. Thyroid medicines can help keep the right level of thyroid hormones in your body. Your provider gives you blood tests during pregnancy to check your TSH and T4 levels to make sure your medicine is at the right amount (also called dose). T4 is a hormone made by your thyroid.

If you’re taking medicine for a thyroid condition before pregnancy, talk to your provider before you get pregnant. Your provider may want to adjust or change your medicine to make sure it’s safe for your baby. If you’re already taking thyroid medicine when you get pregnant, keep taking it and talk to your provider about it as soon as possible.

Treating hyperthyroidism. If you have mild hyperthyroidism, you may not need treatment. If it’s more severe, you may need to take an antithyroid medicine. This medicine causes your thyroid to make less thyroid hormone.

Most providers treat pregnant women with an overactive thyroid with antithyroid medicines called propylthiouracil in the first trimester and methimazole in the second and third trimesters. The timing of these medicines is important. Propylthiouracil after the first trimester can lead to liver problems. And methimazole in the first trimester may increase the risk of birth defects. Birth defects are health conditions that are present at birth. They change the shape or function of one or more parts of the body. Birth defects can cause problems in overall health, how the body develops, or how the body works.

Providers sometimes use radioactive iodine to treat hyperthyroidism. Pregnant women shouldn’t take this medicine because it can cause thyroid problems in the baby.

Antithyroid medicines are safe to take at low doses while you’re breastfeeding.

Treating hypothyroidism. Levothyroxine is the most common medicine used to treat an underactive thyroid during pregnancy. Levothyroxine replaces the thyroid hormone T4, which your own thyroid isn’t making or isn’t making enough of. It’s safe to take this medicine during pregnancy. Thyroid medicines that contain the T3 hormone aren’t safe to use during pregnancy.  

If you had hypothyroidism before getting pregnant, you most likely need to increase the amount of medicine you take during pregnancy. Talk to your health care provider about your medicine as soon as you find out you’re pregnant. Your provider can check to make sure you’re taking the right dose by checking your TSH levels during pregnancy.

Talk to your provider about taking levothyroxine or other medicine to treat hypothyroidism while breastfeeding.

More information

• American Thyroid Association
• MotherToBaby

Last reviewed: February, 2019

See also: Prescription medicine during pregnancy