Thyroid and Pregnancy

The thyroid is a small, butterfly-shaped gland found in the lower part of the neck, just below the voice box. Hormones released by the thyroid control the body’s growth and metabolism. They affect key physical processes like heart rate, digestion, weight, cholesterol and temperature.[1] The thyroid plays a very important role in pregnancy – both in the health of the parent and the development of the baby.[2]

Thyroid dysfunction causes the production of too much or too little thyroid hormone, affecting the body’s processes. This can negatively impact the health of pregnant people and their babies, potentially leading to a number of complications if the condition is not effectively managed.

Undiagnosed or poorly managed thyroid conditions can also make it difficult for one to fall pregnant. However, with proper monitoring and treatment, many people with thyroid disorders are able to have a healthy pregnancy and baby.[3][4]

Some people have a thyroid condition prior to becoming pregnant, while others may develop one during pregnancy or shortly after delivery of the baby. It is recommended that everybody with a thyroid condition, as well as those at increased risk of developing a thyroid condition, consult with a medical practitioner both before trying to conceive and immediately upon falling pregnant.[5]

One is at increased risk of developing a thyroid condition if one:

  • Has had previous medical problems related to the thyroid
  • Has type 1 diabetes or another autoimmune condition
  • Has a family history of thyroid conditions

Read more about Thyroiditis »

Thyroid function in pregnancy

A pregnant body needs to produce more thyroid hormone than usual.[5] A developing fetus is fully dependent on its maternal supply of thyroid hormone until around 12 weeks, and is still partially dependent when its thyroid starts to function independently.[6] Normal levels of thyroid hormone are essential for the healthy development of the baby’s brain and nervous system.[2]

Thyroid hormone levels typically fluctuate during pregnancy (in all pregnancies, regardless of whether a thyroid disorder is present), which can make it difficult to interpret the results of thyroid function blood tests. In addition, the thyroid gland may slightly increase in size during pregnancy. Because this and several of the other possible symptoms of thyroid disorders, such as tiredness and weight gain, are commonly found in pregnancy, it is sometimes difficult to identify thyroid conditions in pregnant people.[2][7]

Hypothyroidism and pregnancy

Hypothyroidism is a condition where an individual’s levels of thyroid hormone are too low. While it is not very common in pregnancy overall, it is more common than hyperthyroidism, where an individual’s levels of thyroid hormone are too high.[8]

Symptoms

The signs and symptoms of hypothyroidism during pregnancy may include, among others:[2][9]

  • Fatigue (generally feeling tired or weak)
  • Depression
  • Forgetfulness
  • Sensitivity to cold
  • Dry skin
  • Poor exercise tolerance
  • Constipation
  • Unexplained weight gain
  • Brittle nails
  • Hair loss
  • Tongue enlargement (swelling)

Because many of these symptoms are experienced during the course of a typical pregnancy, even in people without hypothyroidism, they may be overlooked by a healthcare practitioner. If any of these symptoms are present and an individual is concerned that they may have an undiagnosed thyroid condition, it is recommended that they make this known to their healthcare practitioner.

Some people may have no apparent symptoms, but present with a mild form of hypothyroidism called subclinical hypothyroidism. If this is detected in a blood test, treatment with thyroid hormone replacement medication (usually levothyroxine) may be recommended to help prevent complications during pregnancy.[2][10]

Causes

An underactive thyroid in pregnancy is most commonly caused by Hashimoto’s thyroiditis – an autoimmune condition in which an individual’s immune system mistakenly attacks the thyroid gland.[2]

Hypothyroidism in pregnancy can also arise from a number of other causes, including:[8]

  • Suboptimal (not as good as needed) treatment of an existing thyroid disorder
  • Iodine deficiency
  • Certain medications (such as lithium and amiodarone)

Diagnosis

A doctor will typically take the individual’s medical history and perform a physical examination, then request blood tests to check the levels of thyroid hormone.[2] Low levels of thyroid hormone may indicate that hypothyroidism is present.

Treatment

Hypothyroidism in (and outside of) pregnancy is usually treated with levothyroxine – a synthetic (lab-created) thyroid hormone identical to that produced by the thyroid gland. If it is the first time the affected individual is taking levothyroxine, they will typically be given a starting dose and then have it increased at two- to six-week intervals as necessary, until their thyroid hormones are in the optimal range.[8][11][12]

People who are already taking levothyroxine will typically need to increase their dose during pregnancy to meet the increased need for thyroid hormone. They will also need to have their thyroid hormone levels tested approximately every two to eight weeks. After delivery, the dose can generally be lowered back to its pre-pregnancy level and thyroid hormone levels checked after six to eight weeks.[8][12] A healthcare practitioner or endocrinologist (doctor specializing in hormone-related-conditions) will advise on when it is safe to reduce the dose.

Complications

If it is not properly managed, hypothyroidism in pregnancy can lead to a number of possible complications for both the parent and baby. These may include:[2][8]

  • Preeclampsia (a potentially serious condition characterized by high blood pressure and protein in the urine of the mother)[13]
  • Anemia (low count of red blood cells)
  • High blood pressure[12]
  • Congestive heart failure (rare)
  • Cognitive and developmental difficulties in the baby[3]
  • Low birth weight of the baby
  • Miscarriage
  • Stillbirth

Improperly treated hypothyroidism can also make it difficult to conceive.[4] However, with appropriate treatment, it is generally possible to have a safe and healthy pregnancy.[4][8]

It is recommended that individuals with existing hypothyroidism, or at high risk of developing hypothyroidism, consult with a healthcare practitioner prior to trying to conceive, so that their thyroid hormone levels can be optimized to help ensure a healthy pregnancy.[4]

Hyperthyroidism and pregnancy

Hyperthyroidism is a condition where an individual’s levels of thyroid hormone are too high. It is less common in pregnancy than hypothyroidism.[8]

Symptoms

The signs and symptoms of hyperthyroidism during pregnancy may include, among others:[2][8][14][15]

  • Anxiety or nervousness
  • Irritability
  • Increased sweating
  • Heat intolerance
  • Weight loss or difficulty gaining weight, despite a good appetite
  • Insomnia (sleeplessness)
  • Racing heart or palpitations (pronounced awareness of one’s heartbeat)[16]
  • High blood pressure
  • Increased frequency of bowel movements
  • Nausea and vomiting
  • Fatigue (generally feeling tired or weak)
  • Tremors (shaky hands)
  • Feeling of weakness in the muscles (particularly in the upper arms and thighs)
  • Difficulty exercising
  • Eye bulging and irritation

Some people may experience weight gain due to increased appetite in hyperthyroidism.

Because some of these symptoms can be experienced in pregnancy without hyperthyroidism, they may be overlooked by a healthcare practitioner. If any of these symptoms are present and an individual is concerned that they may have an undiagnosed thyroid condition, it is recommended that they make this known to their healthcare practitioner.

Causes

The most common cause of hyperthyroidism in pregnancy is Grave’s disease – an autoimmune condition in which an individual’s immune system mistakenly stimulates the thyroid gland to produce excessive thyroid hormone. Hyperthyroidism during pregnancy can also, rarely, arise from hyperemesis gravidarum – a condition that causes severe nausea and vomiting during the first few months.[2]

Diagnosis

A doctor will typically take the individual’s medical history and perform a physical examination, then request blood tests to check the levels of thyroid hormone.[2] High levels of thyroid hormone may indicate that hyperthyroidism is present.

Treatment

Mild hyperthyroidism in pregnancy typically does not require treatment. If the hyperthyroidism is more severe, it is usually treated with low doses of antithyroid medications, which reduce the production of thyroid hormone. In the first trimester, propylthiouracil is usually prescribed. In the second and third trimesters, the medication may be changed to methimazole or carbimazole to minimize the risk of toxicity.[2][16]

It will typically be necessary for a person with hyperthyroidism to have their thyroid hormone levels tested frequently during the pregnancy, and their medication adjusted as needed. It may be possible to lower the dose or even stop taking the medication during the third trimester, as Grave’s disease sometimes goes into remission.[16] Approximately six weeks after delivery,[11] a doctor will typically check the person’s thyroid hormone levels again and advise on the treatment or treatment regimen changes necessary, if any.

In rare cases, surgery may be considered to remove all or part of the thyroid gland. This is usually only considered where the individual cannot tolerate antithyroid drugs. Radioactive iodine treatment, while sometimes used in the management of hyperthyroidism, is not a safe option for pregnant people because of the risk of damage to the baby’s thyroid gland.[2][16]

Complications

If it is not properly managed, hyperthyroidism in pregnancy can lead to a number of possible complications for both the parent and baby. These may include:[2][16]

  • Preeclampsia (a potentially serious condition characterized by high blood pressure and protein in the urine of the mother)[13]
  • High blood pressure
  • Congestive heart failure
  • Thyroid storm (sudden, severe worsening of hyperthyroid symptoms)
  • Fetal tachycardia (fast heart rate of the baby)
  • Thyroid problems in the baby[5]
  • Low birth weight of the baby
  • Premature birth
  • Miscarriage
  • Stillbirth

Improperly treated hyperthyroidism can also make it difficult to conceive.[4] However, with appropriate treatment, it is generally possible to have a safe and healthy pregnancy.[4][16]

It is recommended that people with existing hyperthyroidism or a high risk of developing hyperthyroidism consult with a healthcare practitioner prior to trying to conceive, so that their thyroid hormone levels can be optimized to help ensure a healthy pregnancy.[4]

Other types of thyroid problems during pregnancy

While less common, a number of other types of thyroid conditions may affect pregnant people (without necessarily being related to the pregnancy). These include acute infectious thyroiditis, De Quervain’s thyroiditis, Riedel’s thyroiditis and several other thyroid disorders.[8] Treatment will depend on the type and severity of the disorder. If any thyroid condition is suspected, it is important to consult with a healthcare practitioner without delay.

Postpartum thyroiditis

Also known as silent thyroiditis, postpartum thyroiditis is a condition sometimes experienced by individuals who have recently (that is, within the last 12 months) given birth, or had a miscarriage or medical abortion.[17]

Factors which increase one’s risk of developing postpartum thyroiditis include:[5][18]

  • A prior history of thyroid dysfunction
  • Autoimmune conditions (such as type 1 diabetes)
  • Positive tests for thyroid antibodies
  • A family history of thyroid conditions

Thought to be autoimmune in nature, postpartum thyroiditis is a type of inflammation of the thyroid gland. It commonly presents as hypothyroidism, but can also take the form of hyperthyroidism, or a hyperthyroid phase followed by hypothyroidism. Usually, the thyroid function returns to normal.[19][20]

If present, the hyperthyroid phase typically occurs between one and four months after the delivery of the baby and persists for 1-3 months. Symptoms, which include anxiety, difficulty sleeping, tiredness, irritability and a racing heart, among the others listed under Symptoms of hyperthyroidism above, may mistakenly be attributed to the stress of having a newborn.[19]

Treatment will depend on the severity of symptoms. Antithyroid medications will generally not be used, but beta-blockers (a class of medication acting on the heart, blood vessels and kidneys, among other parts of the body) may be prescribed to provide relief from some of the symptoms of hyperthyroidism, like a fast heart rate, anxiety or trembling hands (tremor).[5][19][20]

If present, the hypothyroid phase typically develops between four and eight months after delivery, and may persist for up to 12 months. Symptoms include depression, tiredness, weight gain, constipation and dry skin, among the others listed under Symptoms of hypothyroidism above.[19]

As some of the symptoms are characteristic of the condition known as postpartum blues (the fatigue, lethargy and moodiness that can be experienced after delivery) or postpartum depression, the hypothyroidism can be difficult to recognize. If any symptoms present, it is important to consult with a healthcare practitioner.[2][5]

If the hypothyroidism is mild, treatment may not be necessary, but in more severe cases levothyroxine may be prescribed for six to 12 months. Thereafter, the medication will usually be tapered to assess whether it is still needed.[5][18] In most cases, thyroid function will return to normal within 12-18 months. However, in some people the hypothyroidism will be permanent, and lifelong treatment with levothyroxine may be necessary.[2][19]

In general, individuals who have had postpartum thyroiditis will typically be screened once a year to check that their thyroid hormone levels are normal, as they are at an increased risk of developing permanent hypothyroidism later.[5]

If a person who has been pregnant presents with symptoms of hyperthyroidism after delivery, a doctor will typically run tests to make sure that they do not have Grave’s disease or another condition that requires different treatment to postpartum thyroiditis.[5][12]

Thyroid and pregnancy FAQs

Q: Can thyroid problems affect fertility?
A: Yes. An undiagnosed or poorly-controlled thyroid condition can make it difficult to conceive. This is the case with both hypothyroidism and hyperthyroidism. However, a well-managed thyroid condition will not usually cause difficulties.[4]

Q: Is it safe to take thyroid medication during pregnancy?
A: Yes, as long as it is taken as prescribed by a doctor. Medications used to treat hyperthyroidism need to be prescribed carefully to minimize the risk of side-effects to the mother and baby. Doctors will often prescribe propylthiouracil, if it is available, during the first trimester of pregnancy. This medication is less likely to cause birth defects than the other major antithyroid medication, methimazole, but may have more side-effects and, in rare cases, result in liver damage in the mother. To reduce this risk, doctors often switch to methimazole, if medication is still needed, from the second trimester onwards (when it is considered safe to do so). However, birth defects are rare with either medication. In all cases, the lowest possible dose of antithyroid medication is prescribed to avoid the baby’s thyroid function being impaired. Levothyroxine, the medication most commonly used to treat hypothyroidism, is safe provided it is taken as indicated.[2][21]

Q: Can one breastfeed one’s baby while taking thyroid medication?
A: Yes, provided that they consult with a doctor. Levothyroxine is typically safe for use during breastfeeding, as long as it is taken as prescribed.[4] Antithyroid medication is also generally considered safe for use during breastfeeding, as very little is excreted in the breast milk.[11] However, it may be necessary to adjust the time that the medication is taken, as well as the dose. It may also be necessary for the baby’s thyroid function to be tested from time to time to make sure that its thyroid hormone levels are normal.[4]

Q: Should a pregnant person who is generally healthy take an iodine supplement?
A: In many cases, yes. The American Thyroid Association recommends iodine supplementation during pregnancy and lactation for people in the United States and Canada.[22] Supplementation is also recommended in Germany by the German Society of Internal Medicine, and by a number of other health authorities in other parts of the world. Iodine is found in many prenatal vitamin and mineral supplements. Before taking any such supplements, however, it is advisable to consult with a healthcare practitioner.[23]

Q: Should a pregnant person with a thyroid condition take iodine supplements?
A: Not without consulting a healthcare practitioner. While iodine is important for the healthy functioning of the thyroid gland, it is possible that supplementation may worsen existing thyroid conditions. Before taking any supplements containing iodine, it is recommended that pregnant people with thyroid conditions always speak to a doctor.[2]


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  2. National Institute of Diabetes and Digestive and Kidney Diseases. “Thyroid Disease & Pregnancy.” December, 2017. Accessed November 30, 2017.

  3. Melbourne Thyroid Centre. “Thyroid & Pregnancy.” Accessed November 30, 2017.

  4. British Thyroid Foundation. “Pregnancy and Fertility in Thyroid Disorders.” 2015. Accessed November 30, 2017.

  5. American Family Physician. “Thyroid Disease in Pregnancy.” February, 2014. Accessed November 30, 2017.

  6. Misra, S. (Ed) [“Thyroid Dysfunction and Pregnancy - ECAB.”] 2012. India: Elsevier Health Sciences.

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  8. Patient. “Thyroid Disease In Pregnancy.” June 24, 2016. Accessed December 2, 2017.

  9. American Thyroid Association. “Hypothyroidism (Underactive).” Accessed January 27, 2018.

  10. Thyroid Awareness. “The Thyroid and Pregnancy.” Accessed December 2, 2017.

  11. Obstetrics and Gynecology Clinics of North America. “Diagnosis and Management of Thyroid Disease in Pregnancy.” 2010. Accessed December 4, 2017.

  12. Thyroid UK. “Lothian Guidance for Diagnosis and Management of Thyroid Dysfunction in Pregnancy.” Accessed December 4, 2017.

  13. NHS Choices. “Pre-eclampsia.” June 2, 2015. Accessed December 5, 2017.

  14. American Thyroid Association. “Hyperthyroidism (Overactive).” Accessed January 27, 2018.

  15. American Thyroid Association. “Thyroid & Weight.” 2016. Accessed January 27, 2018.

  16. Patient. “Hyperthyroidism in Pregnancy.” December 23, 2015. Accessed December 4, 2017.

  17. American Family Physician. “Thyroiditis: An Integrated Approach.” September 15, 2014. Accessed December 5, 2017.

  18. American Thyroid Association. “Pregnancy and Thyroid Disease.” Accessed December 6, 2017.

  19. American Thyroid Association. “Postpartum Thyroiditis.” Accessed January 27, 2018.

  20. Journal of Clinical Endocrinology & Metabolism. “Postpartum Thyroiditis.” September 1, 2002. Accessed January 27, 2018.

  21. UpToDate. “Patient education: Antithyroid drugs (Beyond the Basics).” March 15, 2017. Accessed January 28, 2018.

  22. Thyroid. “Iodine Supplementation for Pregnancy and Lactation — United States and Canada: Recommendations of the American Thyroid Association.” 2006. Accessed January 27, 2018.

  23. National Institutes of Health: Office of Dietary Supplements. “Iodine: Fact Sheet for Health Professionals.” June 24, 2011. Accessed January 27, 2018.