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Thyroid During Pregnancy: Everything you Need to Know


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The thyroid is a small butterfly-shaped gland that rests on the base of the neck. The thyroid secretes thyroid hormones that regulate metabolism and control how the organs function, including the heart. 

The imbalance of thyroid hormones can indicate dysregulation and dysfunction of the thyroid gland. Thyroid disorders are a group of diseases caused by the improper functioning of the thyroid gland. 

Maintaining optimal thyroid levels is crucial. Sometimes, the thyroid generates too little or excess thyroid. 

  • Too much thyroid production causes hyperthyroidism,
  • Very less thyroid production leads to hypothyroidism.

Even if you have thyroid problems, you can have a healthy pregnancy while protecting your child’s health with thyroid medications and regular thyroid check-ups. This article explores everything about thyroid, hypo, and hyperthyroidism in pregnancy. 

What is thyroid in pregnancy?

Thyroid hormones, secreted by the thyroid gland, are crucial during pregnancy. They promote normal growth of the baby’s nervous system and brain. 

The thyroid hormone passes through the placenta during the first trimester or the initial 12 weeks. At 12 weeks of pregnancy, the baby’s thyroid will be fully developed and starts making thyroid hormones by 18-10 weeks of pregnancy.  

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), thyroid hormones are usually high in pregnant women and can be difficult to diagnose. 

Pregnancy hormones, such as human chorionic gonadotropin (hCG) and oestrogen, cause an increase in thyroid hormone levels in the blood, and the symptoms that occur are very similar to that of pregnancy. Thyroid glands get enlarged during pregnancy but not significant enough for a diagnosis through a physical examination. 

According to statistics, thyroid dysfunction can affect nearly 2 to 3% of pregnancies. Pregnant women can generally have one of the three below thyroid conditions.

  • Hyperthyroidism, 
  • Hypothyroidism,
  • Postpartum thyroiditis occurs after childbirth. 

Hyperthyroidism in pregnancy

A slight increase in thyroid during pregnancy is normal. However, too many thyroid levels lead to hyperthyroidism or overactive thyroid in pregnancy


Signs and symptoms of hyperthyroidism in pregnancy that are considered normal are:

  • Increased heart rate,
  • Fatigue or tiredness,
  • Trouble dealing with heat.

The other hyperthyroid symptoms that are unusual are:

  • Fast and irregular heart rate,
  • Shivering or shaky hands,
  • Sudden weight loss or 
  • Difficulty in having a normal pregnancy (weight gain)


The most common cause of hyperthyroidism in pregnancy is an autoimmune disorder called Grave’s disease. This autoimmune disorder occurs in 1-4 of 1000 pregnancies, where the immune system creates antibodies called thyroid stimulating immunoglobulin (TSI) that dictate the thyroid to secrete more thyroid hormone. 

Grave’s disease can occur during pregnancy. However, if one has Grave’s disease, during the second and third trimesters, the immune system gets less active, causing less TSI production in the later pregnancy. 

Nonetheless, during the first trimester, the symptoms may get worse, and TSI levels may shoot up. And increased thyroid hormone levels can harm the health of the mother and the baby. 

The second rare cause of hyperthyroidism is extreme morning sickness– severe nausea and vomiting. These early pregnancy symptoms can cause weight loss and dehydration. Experts believe that high levels of hCG early in pregnancy can cause the thyroid to make too much thyroid hormone. However, this hyperthyroidism type goes away during the second and third trimesters. 

Hyperthyroidism can also be due to lumps or nodules in the thyroid gland that causes excess thyroid hormone production. 

Effect on the mother and baby

Hyperthyroidism, if left untreated during pregnancy, can cause pregnancy complications such as,

  • Miscarriage or early pregnancy loss
  • Premature birth
  • Baby with low birthweight
  • Preeclampsia- increased blood pressure in late pregnancy
  • A sudden worsening of thyroid symptoms.
  • Heart failure.

Though Grave’s disease rarely affects the baby, if you have had a radioactive iodine treatment that destroys the thyroid cells or surgery to remove the thyroid, Your body will continue TSI antibody production that may travel into the baby’s bloodstream. Thus causing the baby’s thyroid to produce too much thyroid. Overactive thyroid in the foetus can cause:

  • Increased heart rate or heart failure
  • premature closing of the soft spot in the baby’s skull
  • Low weight gain

The thyroid glands also may get enlarged, pressing against the baby’s windpipe, causing breathing difficulties for the baby. And so, if you have Grave’s disease, your doctor will carefully monitor your pregnancy and your child’s health. 


Diagnosis of overactive thyroid in pregnancy includes a review of the symptoms, physical examination, and blood tests that measure the thyroid levels in the body. Your doctor may also order a TSI antibody test to rule out Grave’s disease.   


Mild overactive thyroid during pregnancy requires no treatment. But, if hyperthyroidism is due to excess hCG hormones, the treatment will focus on reducing morning sickness symptoms. 

For severe hyperthyroidism, antithyroid medications may reduce thyroid hormone production. However, if the thyroid hormones are passed on to the baby’s bloodstream, you will need to see an endocrine specialist or maternal-foetal medicine specialist for treatment and continuous monitoring.  

Hypothyroidism in pregnancy

If your body is making less than the required thyroid levels, you may have hypothyroidism. Hypothyroidism or underactive thyroid in pregnancy can reduce the body’s metabolic activity. 


Signs and symptoms of underactive thyroid in pregnancy may not be detected or can be mild, including: 

  • extreme tiredness or fatigue,
  • trouble dealing with cold,
  • Severe muscle cramps,
  • severe constipation
  • Issues with memory or concentration


The prime cause of hypothyroidism in pregnancy is an autoimmune disorder called Hashimoto’s disease that occurs in 2-3 of 100 pregnancies. In this disorder, the immune system generates antibodies that attack and destroy the thyroid, causing swelling, damage, and low thyroid production.

Effect on the mother and baby

An untreated hypothyroidism during pregnancy can cause,

  • Preeclampsia- an increase in blood pressure in the later pregnancy,
  • Anaemia,
  • Pregnancy loss,
  • Baby with low birth weight, 
  • Stillbirth, and
  • Rarely, a heart failure. 

In the first trimester, thyroid hormones are crucial for the baby’s brain and nervous system. And so, low thyroid production in the mother can lead to low IQ, neurological defects, and developmental issues in the baby. 


Diagnosis includes a detailed review of symptoms. The other investigative tests of low thyroid levels in pregnancy include:

  • Blood tests to measure thyroid levels,
  • Antibody test to rule out Hashimoto’s disease


Treatment for hypothyroidism in pregnancy includes thyroid replacement therapy with thyroid medications and regular monitoring of thyroid levels. However, pregnant women with mild forms of hypothyroidism may not require treatment. 

Postpartum thyroiditis in pregnancy

Postpartum thyroiditis occurs during the first year of childbirth. It is an inflammation of the thyroid gland and can affect nearly 1-2 in 22 women post-pregnancy. 

The thyroid inflammation initially causes leakage of thyroid hormones, increasing their production. Hence, there will be a rise in thyroid levels for about three months of delivery. 

Later, prolonged inflammation can damage the thyroid glands, causing hypothyroidism that can last up to a year after childbirth. Sometimes, the underactive thyroid does not go away even after a year. Some may go through only the hyperthyroid phase, while some have only the hypothyroid phase. However, very rarely do women go through both postpartum thyroiditis phases.  


Postpartum thyroiditis seldom shows any symptoms or is mild. Hyperthyroidism symptoms get prominent when the thyroid is overactive. And one can observe hypothyroidism signs when the thyroid is underactive. 

If the symptoms occur during the early postpartum period, one may have symptoms of postpartum depression.   


Postpartum thyroiditis is commonly linked to an autoimmune condition similar to Hashimoto’s disease. This autoimmune condition may be mild during or before pregnancy and can flare up post-pregnancy, causing postpartum thyroiditis. 


Diagnosis of postpartum thyroiditis includes blood tests to check thyroid levels. 


The hyperthyroid phase of postpartum thyroiditis is usually mild and does not require any treatment. Sometimes, beta blockers are prescribed to reduce thyroid production. However, if the hyperthyroidism is due to a pre-existing Grave’s disease, your doctor may prescribe antithyroid medications.  

Treatment for the hypothyroid phase includes thyroid hormone medications to alleviate thyroid symptoms.  

Frequently Asked Questions

Is it safe to breastfeed while on thyroid hormone treatment or antithyroid medicines?

Most thyroid hormone medications are safe. Though a small amount of them can reach the baby through breastmilk, it is safe for the baby. However, your doctor will reduce or limit the dosage if you take antithyroid drugs. For beta-blockers in postpartum thyroiditis, certain beta blockers are safe to be used while breastfeeding. 

How can I control my thyroid during pregnancy?

Along with medications and treatment, you can always control your thyroid during pregnancy with the following tips. 

  • Eat healthy foods and avoid foods that can affect the thyroid,
  • Have your meals on time,
  • Get enough vitamin D,
  • Include whole grains, green leafy vegetables, nuts, and berries in your diet,
  • Moderately exercise regularly, as suggested by your doctor, 
  • Follow healthy sleep hygiene. 

What foods can I eat during pregnancy to keep my thyroid working well? 

Thyroid function depends on the iodine intake in the body. Your baby can get iodine from your diet, and you will need around 250 micrograms of iodine per day during pregnancy. You can get iodine from natural sources like dairy products, seafood, eggs, iodised salt, and poultry. 


The thyroid gland is an essential butterfly-shaped gland that makes thyroid hormones. The thyroid hormones control metabolism and help organs function effectively. Too less or too much thyroid hormones in the body can lead to hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) even during pregnancy. 

Untreated hyper or hypothyroidism in pregnancy can cause critical issues, like premature birth, miscarriage, low birth weight, and stillbirth. Thyroid conditions diagnosed and treated during pregnancy can help healthy pregnancy and protect the baby’s health. 

Get regular thyroid checks done even in pregnancy, eat healthily and consult your doctor if you observe even one symptom of thyroid conditions during pregnancy.

Srujana Mohanty
She is the Managing Editor of Cogito137, one of India’s leading student-run science communication magazines. She's been working in scientific and medical writing and editing since 2018, also associated with the quality assurance team of scientific journal editing. Majored in Chemistry with a minor in Biology at IISER Kolkata, Srujana loves doodling and watching series.


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