Hyperthyroidism is estimated to occur in 0.1% to 0.4% of pregnancies.¹ The thyroid gland produces hormones that control how the body uses energy. These thyroid hormones affect the function of all major organs in the body.
Sometimes the thyroid produces too many hormones, resulting in hyperthyroidism. This condition, most commonly caused by Graves’ disease, speeds up many bodily functions.
Pregnancy usually increases the need for thyroid hormones, causing the thyroid gland to enlarge slightly. That, combined with the fact that hyperthyroidism shares similar symptoms with thyroid disorders, makes it difficult to diagnose hyperthyroidism during pregnancy.
If left untreated, hyperthyroidism can result in serious health complications involving the bones and heart. Untreated thyroid disorders during pregnancy have also been linked to miscarriage, premature birth, and stillbirth. Therefore, it is important to treat thyroid conditions to help ensure a healthy pregnancy and baby.
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Hyperthyroidism is a relatively common condition to experience during pregnancy, and it requires immediate treatment. This is because proper thyroid hormone production is crucial for the healthy development of the fetal nervous system and brain, especially during the first trimester.
A fetus gets thyroid hormones from its mother until around 12 weeks into the pregnancy. At this point, the fetus’ thyroid gland starts producing its own hormones. However, it doesn't produce enough thyroid hormones until around 18 to 20 weeks.
Increased levels of thyroid hormones during pregnancy can occur for several reasons, including:
The leading cause of hyperthyroidism in pregnancy is Graves' disease. This autoimmune condition develops when the immune system produces antibodies that cause the thyroid gland to make too much of the thyroid hormone.
A common symptom of Graves' disease is an enlarged thyroid gland. In some cases, the condition affects the eyes, with some patients experiencing a gritty sensation, double vision, increased tear production, and difficulty closing the eyelids.
Pregnant women with Graves' disease are at a higher risk of miscarriage, premature birth, and low birth weight.
Hyperemesis gravidarum is extreme and persistent nausea and vomiting during pregnancy. It causes dehydration, electrolyte imbalances, and weight loss.
This condition is more severe than typical morning sickness and results from elevated human chorionic gonadotropin (HCG) levels in early pregnancy.
HCG is the same hormone measured to determine whether you are pregnant via a urine pregnancy test. If HCG levels are too high, the thyroid gland produces too much of the thyroid hormone.
However, this type of hyperthyroidism usually resolves during the second trimester of pregnancy.
Hyperfunctioning thyroid nodules
Sometimes the nodules in the thyroid gland produce more hormones than the body needs, which can also lead to hyperthyroidism in pregnancy.
Less common causes of hyperthyroidism include:
Subacute thyroiditis — A painful thyroid inflammation caused by a virus.
Postpartum thyroiditis — A form of thyroiditis that develops shortly after birth and usually lasts between one to two months.
Lymphocytic thyroiditis — A painless thyroid inflammation that occurs when lymphocytes or white blood cells accumulate in the thyroid gland.
Certain medications and cancer immunotherapies — These have also been linked to hyperthyroidism in some cases.
You may be at a higher risk of developing hyperthyroidism in pregnancy² if any of the following criteria apply to you:
You're currently undergoing treatment for thyroid disease, goiter, or you have thyroid nodules.
You have a family history of Graves' disease or other autoimmune disorders.
You had had a thyroid condition before or gave birth to a baby with a thyroid disorder.
You have type 1 diabetes.
You have previously had high-dose neck radiation treatment for hyperthyroidism.
You have previously had miscarriages or preterm deliveries
Ask your healthcare provider to test you for hyperthyroidism if you have a history of thyroid disease or are otherwise at risk of hyperthyroidism.
During pregnancy, common symptoms of hyperthyroidism include:
Increased heart rate (tachycardia)
Severe nausea and vomiting
Some patients may also experience confusion and/or a rare, life-threatening condition called a thyroid storm, which refers to an abnormal increase in metabolism. This is usually precipitated by gestational trophoblastic disease, labor, cesarean section, or infection. Pregnant women affected by thyroid storm are at a high risk of heart failure.
As hyperthyroidism shares many similar symptoms with other health conditions, it is essential to consult an endocrinologist for an accurate diagnosis.
Throughout the pregnancy, you must also monitor your thyroid levels to ensure you do not develop hyperthyroidism symptoms and treat them if you do.
Differences between hyperthyroidism and hypothyroidism
Whereas hyperthyroidism refers to an overactive thyroid gland, hypothyroidism occurs when the thyroid gland is underactive and doesn't produce enough thyroid hormones.
These conditions share some similar symptoms, such as enlargement of the thyroid gland. However, they are two distinct conditions and have their own symptoms.
People with hyperthyroidism tend to experience higher energy levels as opposed to people with hypothyroidism who experience decreased energy levels.
Because of increased metabolism, hyperthyroidism also causes weight loss and anxiety. The reduced metabolism caused by hypothyroidism results in tiredness, weight gain, and depression.
Because of the risks associated with hyperthyroidism, thyroid levels should be monitored before and throughout the pregnancy, especially if you are at risk of thyroid disease.
If left untreated, hyperthyroidism during pregnancy can lead to several complications for both the mother and baby before and after birth.
This is a complication of pregnancy that is usually characterized by elevated blood pressure and damage to the liver, kidneys, or other organs. Preeclampsia tends to develop after 20 weeks during pregnancy. If left untreated, it can cause serious, or even fatal, complications for both mother and baby.
The most effective treatment for preeclampsia is delivering the baby. However, there is a form of preeclampsia called postpartum preeclampsia, which occurs after birth.
Pulmonary arterial hypertension
Hyperthyroidism during pregnancy increases the risk of pulmonary arterial hypertension (PAH), a condition that affects the right side of the heart and the arteries in the lungs.
If you have PAH, the blood vessels in the lungs become damaged, narrow, or blocked. This slows down blood flow through the lungs and forces the heart to work harder to pump blood to the lungs. Over time, the heart muscle weakens, which can result in heart failure.
PAH in pregnant women is associated with a significantly higher mortality rate of between 30% to 56%.³ Symptoms develop slowly and may include:
Shortness of breath
Chest pressure or pain
Bluish color of the skin and lips
Placental abruption occurs when the placenta partially or fully separates from the inner wall of the uterus before delivery. This results in excessive bleeding for the mother and blocks the supply of nutrients and oxygen to the fetus. The condition stunts growth of the baby and reduces amniotic fluid levels.
Placental abruption occurs suddenly and manifests with symptoms like abdominal pain, vaginal bleeding, uterine rigidity or tenderness, back pain, and close uterine contractions. The blood can sometimes become trapped in the uterus, so there may not be any visible bleeding. In some cases, placental abruption develops slowly, causing intermittent vaginal bleeding.
Thyrotoxic crisis, more commonly known as thyroid storm, is triggered by excessive thyroid hormone production. Immediate diagnosis and treatment are essential because the condition is almost always fatal.
Symptoms include neurological and gastrointestinal irregularities, fast heart rate (tachycardia), fever, and high blood pressure (hypertension).
Thyroid storm is a rare condition that develops in hyperthyroidism patients who are not receiving treatment.
Risks for the baby
Untreated hyperthyroidism during pregnancy can also result in the following health complications for the baby.
A full-term pregnancy is measured at 40 weeks. Premature birth is when the baby is born before 37 weeks, and it increases the risk of the baby developing health problems, either at birth or later in life.
Make sure to call your healthcare provider immediately if you notice any of the following symptoms:
Change in vaginal discharge
Pressure in the belly or pelvis
Belly cramps with or without diarrhea
Constant low and dull backache
Your water breaks
Low birth weight
This is when a baby is born weighing less than 5 pounds 8 ounces. While some babies with a low birth weight can be healthy, many have severe health complications that require immediate treatment. These include:
Bleeding in the brain
Patent ductus arteriosus (an extra blood vessel that should close when baby is born)
Retinopathy of prematurity
Ensure that you attend all of your prenatal appointments to track the baby's growth and development and consult your healthcare professional if any issues appear.
Miscarriage or still birth
Miscarriage occurs when the baby dies in the womb before the 20 weeks during pregnancy, whereas a stillbirth is when a baby dies in the womb after 20 weeks.
The antibodies that cause Graves' disease have been known to cross into the baby via the placenta. This increases the baby's risk of developing thyroid conditions both during and after birth. The risk is higher if you have received radioactive iodine treatment for Graves' disease during pregnancy.
It is essential to contact your healthcare provider immediately if you experience a rapid heartbeat, unexplained weight loss, swelling at the base of your neck, or other symptoms associated with hyperthyroidism.
You should clearly describe the specific symptoms you are experiencing because some of them are associated with other conditions, and it is crucial to get the right diagnosis.
Your doctor will likely perform a physical exam and a series of blood tests, known as thyroid function tests (TFTs), to measure your thyroid hormone levels. These tests include:
Free T4 and total T3 test — Both the T3 and T4 thyroid hormones will be incredibly high if you have hyperthyroidism.
TSH test — The pituitary gland releases the TSH hormone if there isn't enough thyroid hormone in the body. Hyperthyroidism causes deficient TSH levels.
Thyrotropin receptor antibody (TRA) test — This test helps to detect the antibody that causes Graves' disease.
Thyroid ultrasound — Your doctor may perform an ultrasound to determine whether the thyroid gland is enlarged and has increased blood flow.
The right treatment for you if you experience hyperthyroidism during pregnancy depends on a range of factors, including the severity of your thyroid problem, your age and physical condition, and whether there may be another underlying cause.
Your doctor may not recommend treatment if you only present symptoms of mild hyperthyroidism.
The most common treatments for hyperthyroidism during pregnancy include the following:
These medications help to lower thyroid hormone production. Propylthiouracil (PTU) is the medication most commonly used by pregnant women during the first trimester.
It is not often used outside of pregnancy because of its associated side effects, such as neck swelling, dizziness, numbness or tingling of the feet, and joint and muscle pain. It can also cause liver problems if administered after the first trimester.
Another form of antithyroid drug, methimazole, is preferred during the second and third trimesters. If administered during the first trimester, methimazole can lead to congenital disabilities.
Surgery is considered a suitable treatment if you cannot be appropriately treated for hyperthyroidism with antithyroid drugs.
A thyroidectomy or surgical removal of the thyroid gland is a permanent solution and is only recommended as a last resort. The procedure is safest during the second trimester.
Radioactive iodine treatment
Many doctors have conflicting views on using radioiodine to treat hyperthyroidism during pregnancy. In general, the consensus is to avoid it during pregnancy if at all possible.
While it does resolve symptoms of hyperthyroidism, it can easily cross the placenta and destroy the baby's thyroid gland, causing permanent hypothyroidism. If this occurs, you may have to take hormone pills to ensure normal hormone levels for the rest of your life.
This form of medication helps control certain symptoms caused by hyperthyroidism like tremors and heart palpitations. Beta-blockers are only used sparingly as long-term use is associated with impaired fetal growth.⁴
Producing the optimal amount of thyroid hormones — not too many or too few — is essential for ensuring maternal and fetal health during pregnancy.
Hyperthyroidism, which occurs due to the overproduction of thyroid hormones, accelerates your body’s energy consumption and speeds up your metabolism. This results in symptoms including unintentional weight loss and irregular or rapid heartbeat, among others.
Unfortunately, it's not easy to diagnose many thyroid problems due to the hormonal demands involved in pregnancy and sharing symptoms with other health conditions.
Hyperthyroidism can be dangerous, causing complications ranging from miscarriage and stillbirth for the baby to preeclampsia and thyroid storm for the mother. The good news is that most people respond well to treatment, which may involve surgery or antithyroid and other medications.
If you are pregnant, especially if you are at risk of developing hyperthyroidism, it is important to attend all prenatal appointments to track your thyroid levels and ensure any thyroid problems are detected and treated early.
Thyroid and pregnancy | American Thyroid Association
Pulmonary hypertension in pregnancy and its prognostic implications | (PVRI) Pulmonary Vascular Research Institute
Treatment of hyperthyroidism in pregnancy | Endocrine Abstracts
Hyperthyroidism in pregnancy (2021)