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\nThyroid disease is a group of disorders that affects the thyroid gland. The thyroid is a small, butterfly-shaped gland in the front of your neck that makes thyroid hormones. Thyroid hormones control how your body uses energy, so they affect the way nearly every organ in your body works\u2014even the way your heart beats.
\n \nSometimes the thyroid makes too much or too little of these hormones. Too much thyroid hormone is called hyperthyroidism and can cause many of your body\u2019s functions to speed up. \u201cHyper\u201d means the thyroid is overactive. Learn more about hyperthyroidism in pregnancy. Too little thyroid hormone is called hypothyroidism and can cause many of your body\u2019s functions to slow down. \u201cHypo\u201d means the thyroid is underactive. Learn more about hypothyroidism in pregnancy.
\nIf you have thyroid problems, you can still have a healthy pregnancy and protect your baby\u2019s health by having regular thyroid function tests and taking any medicines that your doctor prescribes.
\nThyroid hormones are crucial for normal development of your baby\u2019s brain and nervous system. During the first trimester\u2014the first 3 months of pregnancy\u2014your baby depends on your supply of thyroid hormone, which comes through the placenta. At around 12 weeks, your baby\u2019s thyroid starts to work on its own, but it doesn\u2019t make enough thyroid hormone until 18 to 20 weeks of pregnancy.
\nTwo pregnancy-related hormones\u2014human chorionic gonadotropin (hCG) and estrogen\u2014cause higher measured thyroid hormone levels in your blood. The thyroid enlarges slightly in healthy women during pregnancy, but usually not enough for a health care professional to feel during a physical exam.
\nThyroid problems can be hard to diagnose in pregnancy due to higher levels of thyroid hormones and other symptoms that occur in both pregnancy and thyroid disorders. Some symptoms of hyperthyroidism or hypothyroidism are easier to spot and may prompt your doctor to test you for these thyroid diseases.
\nAnother type of thyroid disease, postpartum thyroiditis, can occur after your baby is born.
\nSome signs and symptoms of hyperthyroidism often occur in normal pregnancies, including faster heart rate, trouble dealing with heat, and tiredness.
\nOther signs and symptoms can suggest hyperthyroidism:
\nHyperthyroidism in pregnancy is usually caused by Graves\u2019 disease and occurs in 1 to 4 of every 1,000 pregnancies in the United States.1 Graves\u2019 disease is an autoimmune disorder. With this disease, your immune system makes antibodies that cause the thyroid to make too much thyroid hormone. This antibody is called thyroid stimulating immunoglobulin, or TSI.
\nGraves\u2019 disease may first appear during pregnancy. However, if you already have Graves\u2019 disease, your symptoms could improve in your second and third trimesters. Some parts of your immune system are less active later in pregnancy so your immune system makes less TSI. This may be why symptoms improve. Graves\u2019 disease often gets worse again in the first few months after your baby is born, when TSI levels go up again. If you have Graves\u2019 disease, your doctor will most likely test your thyroid function monthly throughout your pregnancy and may need to treat your hyperthyroidism.1 Thyroid hormone levels that are too high can harm your health and your baby\u2019s.
\n \nRarely, hyperthyroidism in pregnancy is linked to hyperemesis gravidarum\u2014severe nausea and vomiting that can lead to weight loss and dehydration. Experts believe this severe nausea and vomiting is caused by high levels of hCG early in pregnancy. High hCG levels can cause the thyroid to make too much thyroid hormone. This type of hyperthyroidism usually goes away during the second half of pregnancy.
\nLess often, one or more nodules, or lumps in your thyroid, make too much thyroid hormone.
\nUntreated hyperthyroidism during pregnancy can lead to
\nRarely, Graves\u2019 disease may also affect a baby\u2019s thyroid, causing it to make too much thyroid hormone. Even if your hyperthyroidism was cured by radioactive iodine treatment to destroy thyroid cells or surgery to remove your thyroid, your body still makes the TSI antibody. When levels of this antibody are high, TSI may travel to your baby\u2019s bloodstream. Just as TSI caused your own thyroid to make too much thyroid hormone, it can also cause your baby\u2019s thyroid to make too much.
\nTell your doctor if you\u2019ve had surgery or radioactive iodine treatment for Graves\u2019 disease so he or she can check your TSI levels. If they are very high, your doctor will monitor your baby for thyroid-related problems later in your pregnancy.
\n \nAn overactive thyroid in a newborn can lead to
\nSometimes an enlarged thyroid can press against your baby\u2019s windpipe and make it hard for your baby to breathe. If you have Graves\u2019 disease, your health care team should closely monitor you and your newborn.
\nYour doctor will review your symptoms and do some blood tests to measure your thyroid hormone levels. Your doctor may also look for antibodies in your blood to see if Graves\u2019 disease is causing your hyperthyroidism. Learn more about thyroid tests and what the results mean.
\nIf you have mild hyperthyroidism during pregnancy, you probably won\u2019t need treatment. If your hyperthyroidism is linked to hyperemesis gravidarum, you only need treatment for vomiting and dehydration.
\nIf your hyperthyroidism is more severe, your doctor may prescribe antithyroid medicines, which cause your thyroid to make less thyroid hormone. This treatment prevents too much of your thyroid hormone from getting into your baby\u2019s bloodstream. You may want to see a specialist, such as an endocrinologist or expert in maternal-fetal medicine, who can carefully monitor your baby to make sure you\u2019re getting the right dose.
\nDoctors most often treat pregnant women with the antithyroid medicine propylthiouracil (PTU) during the first 3 months of pregnancy. Another type of antithyroid medicine, methimazole, is easier to take and has fewer side effects, but is slightly more likely to cause serious birth defects than PTU. Birth defects with either type of medicine are rare. Sometimes doctors switch to methimazole after the first trimester of pregnancy. Some women no longer need antithyroid medicine in the third trimester.
\nSmall amounts of antithyroid medicine move into the baby\u2019s bloodstream and lower the amount of thyroid hormone the baby makes. If you take antithyroid medicine, your doctor will prescribe the lowest possible dose to avoid hypothyroidism in your baby but enough to treat the high thyroid hormone levels that can also affect your baby.
\nAntithyroid medicines can cause side effects in some people, including
\nStop your antithyroid medicine and call your doctor right away if you develop any of these symptoms while taking antithyroid medicines:
\nIf you don\u2019t hear back from your doctor the same day, you should go to the nearest emergency room.
\nYou should also contact your doctor if any of these symptoms develop for the first time while you\u2019re taking antithyroid medicines:
\nIf you are allergic to or have severe side effects from antithyroid medicines, your doctor may consider surgery to remove part or most of your thyroid gland. The best time for thyroid surgery during pregnancy is in the second trimester.
\nRadioactive iodine treatment is not an option for pregnant women because it can damage the baby\u2019s thyroid gland.
\nSymptoms of an underactive thyroid are often the same for pregnant women as for other people with hypothyroidism. Symptoms include
\nMost cases of hypothyroidism in pregnancy are mild and may not have symptoms.
\nHypothyroidism in pregnancy is usually caused by Hashimoto\u2019s disease and occurs in 2 to 3 out of every 100 pregnancies.1 Hashimoto\u2019s disease is an autoimmune disorder. In Hashimoto\u2019s disease, the immune system makes antibodies that attack the thyroid, causing inflammation and damage that make it less able to make thyroid hormones.
\nUntreated hypothyroidism during pregnancy can lead to
\nThese problems occur most often with severe hypothyroidism.
\nBecause thyroid hormones are so important to your baby\u2019s brain and nervous system development, untreated hypothyroidism\u2014especially during the first trimester\u2014can cause low IQ and problems with normal development.
\nYour doctor will review your symptoms and do some blood tests to measure your thyroid hormone levels. Your doctor may also look for certain antibodies in your blood to see if Hashimoto\u2019s disease is causing your hypothyroidism. Learn more about thyroid tests and what the results mean.
\nTreatment for hypothyroidism involves replacing the hormone that your own thyroid can no longer make. Your doctor will most likely prescribe levothyroxine, a thyroid hormone medicine that is the same as T4, one of the hormones the thyroid normally makes. Levothyroxine is safe for your baby and especially important until your baby can make his or her own thyroid hormone.
\nYour thyroid makes a second type of hormone, T3. Early in pregnancy, T3 can\u2019t enter your baby\u2019s brain like T4 can. Instead, any T3 that your baby\u2019s brain needs is made from T4. T3 is included in a lot of thyroid medicines made with animal thyroid, such as Armour Thyroid, but is not useful for your baby\u2019s brain development. These medicines contain too much T3 and not enough T4, and should not be used during pregnancy. Experts recommend only using levothyroxine (T4) while you\u2019re pregnant.
\nSome women with subclinical hypothyroidism\u2014a mild form of the disease with no clear symptoms\u2014may not need treatment.
\n \nIf you had hypothyroidism before you became pregnant and are taking levothyroxine, you will probably need to increase your dose. Most thyroid specialists recommend taking two extra doses of thyroid medicine per week, starting right away. Contact your doctor as soon as you know you\u2019re pregnant.
\nYour doctor will most likely test your thyroid hormone levels every 4 to 6 weeks for the first half of your pregnancy, and at least once after 30 weeks.1 You may need to adjust your dose a few times.
\nPostpartum thyroiditis is an inflammation of the thyroid that affects about 1 in 20 women during the first year after giving birth1 and is more common in women with type 1 diabetes. The inflammation causes stored thyroid hormone to leak out of your thyroid gland. At first, the leakage raises the hormone levels in your blood, leading to hyperthyroidism. The hyperthyroidism may last up to 3 months. After that, some damage to your thyroid may cause it to become underactive. Your hypothyroidism may last up to a year after your baby is born. However, in some women, hypothyroidism doesn\u2019t go away.
\nNot all women who have postpartum thyroiditis go through both phases. Some only go through the hyperthyroid phase, and some only the hypothyroid phase.
\nThe hyperthyroid phase often has no symptoms\u2014or only mild ones. Symptoms may include irritability, trouble dealing with heat, tiredness, trouble sleeping, and fast heartbeat.
\nSymptoms of the hypothyroid phase may be mistaken for the \u201cbaby blues\u201d\u2014the tiredness and moodiness that sometimes occur after the baby is born. Symptoms of hypothyroidism may also include trouble dealing with cold; dry skin; trouble concentrating; and tingling in your hands, arms, feet, or legs. If these symptoms occur in the first few months after your baby is born or you develop postpartum depression, talk with your doctor as soon as possible.
\nPostpartum thyroiditis is an autoimmune condition similar to Hashimoto\u2019s disease. If you have postpartum thyroiditis, you may have already had a mild form of autoimmune thyroiditis that flares up after you give birth.
\n \nIf you have symptoms of postpartum thyroiditis, your doctor will order blood tests to check your thyroid hormone levels.
\nThe hyperthyroid stage of postpartum thyroiditis rarely needs treatment. If your symptoms are bothering you, your doctor may prescribe a beta-blocker, a medicine that slows your heart rate. Antithyroid medicines are not useful in postpartum thyroiditis, but if you have Grave\u2019s disease, it may worsen after your baby is born and you may need antithyroid medicines.
\nYou\u2019re more likely to have symptoms during the hypothyroid stage. Your doctor may prescribe thyroid hormone medicine to help with your symptoms. If your hypothyroidism doesn\u2019t go away, you will need to take thyroid hormone medicine for the rest of your life.
\nCertain beta-blockers are safe to use while you\u2019re breastfeeding because only a small amount shows up in breast milk. The lowest possible dose to relieve your symptoms is best. Only a small amount of thyroid hormone medicine reaches your baby through breast milk, so it\u2019s safe to take while you\u2019re breastfeeding. However, in the case of antithyroid drugs, your doctor will most likely limit your dose to no more than 20 milligrams (mg) of methimazole or, less commonly, 400 mg of PTU.
\nBecause the thyroid uses iodine to make thyroid hormone, iodine is an important mineral for you while you\u2019re pregnant. During pregnancy, your baby gets iodine from your diet. You\u2019ll need more iodine when you\u2019re pregnant\u2014about 250 micrograms a day.1 Good sources of iodine are dairy foods, seafood, eggs, meat, poultry, and iodized salt\u2014salt with added iodine. Experts recommend taking a prenatal vitamin with 150 micrograms of iodine to make sure you\u2019re getting enough, especially if you don\u2019t use iodized salt.1 You also need more iodine while you\u2019re breastfeeding since your baby gets iodine from breast milk. However, too much iodine from supplements such as seaweed can cause thyroid problems. Talk with your doctor about an eating plan that\u2019s right for you and what supplements you should take. Learn more about a healthy diet and nutrition during pregnancy.
\nThe National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions.
\nClinical trials are part of clinical research and at the heart of all medical advances. Clinical trials look at new ways to prevent, detect, or treat disease. Researchers also use clinical trials to look at other aspects of care, such as improving the quality of life for people with chronic illnesses. Find out if clinical trials are right for you.
\nClinical trials that are currently open and are recruiting can be viewed at www.ClinicalTrials.gov.
\nThis content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by NIDDK is carefully reviewed by NIDDK scientists and other experts.
The NIDDK would like to thank:
Linda Barbour, M.D., M.S.P.H., FACP, University of Colorado School of Medicine