Hyperthyroidism, or an overactive thyroid, can develop during pregnancy. Doctors may have difficulty spotting or diagnosing it, as pregnancy can cause elevated hormone levels and similar symptoms.

During pregnancy, the person’s thyroid needs to produce enough hormones to support both themselves and the developing fetus.

Eventually, the fetus develops its own thyroid that produces the required hormones.

Hyperthyroidism, or overactive thyroid, occurs when the thyroid gland produces too much hormone. It affects about 0.2–0.4% of all pregnancies.

Though rare, doctors may screen for it due to potential complications associated with the pregnant person and developing fetus.

This article reviews hyperthyroidism during pregnancy, possible symptoms, causes, and more.

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The majority of hyperthyroidism cases during pregnancy occur due to Graves’ disease. Graves’ disease is an autoimmune disorder that affects the thyroid, causing an overactive thyroid.

During pregnancy, tissue in the developing placenta creates a hormone called human chorionic gonadotropin (hCG). High levels of hCG are responsible for the feelings of morning sickness.

In rare cases, elevated hCG levels can cause a temporary case of hyperthyroidism during early pregnancy.

Can having a baby cause hyperthyroidism?

Following delivery, a person may develop symptoms of Graves’ disease for the first time, which causes hyperthyroidism. If they had a previous diagnosis, they might experience worsening symptoms in the postpartum period.

It is also possible for a person to develop inflammation of the thyroid after they give birth. This is called postpartum thyroiditis.

The inflammation can lead to hypothyroidism. This means the thyroid will not produce enough hormones for the body’s needs.

The thyroid produces hormones that provide vital functions for several different tissue and organs throughout the body. During pregnancy, they play a crucial role in helping the fetus’ brain’s development.

During the first trimester — 3 months — the fetus relies completely on the hormones from the pregnant person.

After about 12 weeks, the fetus will start to produce hormones on its own, but it will still require hormones from the parent up until about 20 weeks.

Hormones common in pregnancy — hCG and estrogen — can increase the level of thyroid hormones. The thyroid gland may also enlarge slightly.

The symptoms of hyperthyroidism in pregnant people are the same as those in people who are not pregnant. They can also mimic some of the symptoms of early pregnancy.

Hyperthyroidism can cause symptoms that include:

The primary cause of hyperthyroidism is Graves’ disease. Graves’ disease affects about 0.5% of the population. It affects about 1–4 out of 1,000 births in the United States.

It most commonly occurs in people between the ages of 20–40 years. The risk increases with age.

Some people will first experience Graves’ disease during pregnancy. People already living with the condition may notice their symptoms clear for the 2nd and 3rd trimesters, though they could rebound following pregnancy.

Other causes of hyperthyroidism are much less common. For example, thyroid nodules can lead to hyperthyroidism but are not very common in people under the age of 40 years.

This makes it less likely that a person will develop overactive thyroid due to nodules during their pregnancy.

Rising or elevated hCG levels may also lead to temporary cases of hyperthyroidism. However, these cases tend to clear within the first trimester.

Hyperthyroidism can cause issues for the developing fetus. It can include complications such as:

A person should discuss hyperthyroidism treatment with a doctor and follow their advice.

Mild cases may not require any treatment other than extra monitoring to make sure it does not worsen.

For severe cases, a doctor will likely prescribe antithyroid medications to slow the thyroid’s production. They will likely closely monitor the medication and fetus’ health when taking medications for hyperthyroidism.

Thyroid medication and pregnancy

The standard treatment for hyperthyroidism during pregnancy is often propylthiouracil. Doctors typically prescribe it for the first 3 months of pregnancy.

They may also prescribe methimazole, but this has a higher risk of congenital abnormalities. However, congenital abnormalities with this medication are still rare.

A person should stop any medication if they notice any unusual side effects, which can include:

A person may also develop an allergic reaction to medication and should discuss their symptoms with a doctor.

In most cases, a doctor will prescribe the lowest dose possible since the medication can affect the fetus’ thyroid hormone production.

Due to risks to the developing fetus, doctors advise against taking radioactive iodine during pregnancy.

Diagnosis often involves:

  • a physical examination
  • a review of family and personal medical history
  • an examination of a person’s symptoms

Clinicians will also run blood tests to check for thyroid levels and antibodies associated with Graves’ disease.

Doctors can also find other possible causes of hypothyroidism, such as:

  • thyroid nodules
  • a benign tumor
  • thyroiditis
  • excess iodine

Treatment can help a person and fetus avoid potential complications associated with hyperthyroidism.

Complications can be potentially serious and include:

A person with hypothyroidism should follow up with a doctor if they take an at-home pregnancy test and receive positive results.

A doctor can help confirm the pregnancy and develop a plan for managing the pregnancy and hypothyroidism. A person may need to change their medication while they are pregnant.

If someone without a known thyroid issue experiences symptoms of a thyroid issue during pregnancy, they should contact a doctor. A doctor can help determine if the new symptoms require medical attention.

In most cases, a person should discuss with a doctor before stopping any medication. However, if a person develops the following symptoms, they should stop their medication and talk with a doctor as soon as possible:

  • fever
  • dull pain in the abdomen
  • yellowing of skin or whites of the eyes
  • constant sore throat

A person should also contact a doctor if they develop any of the following symptoms for the first time after taking any medications for hyperthyroidism:

The following sections provide answers to common questions about hyperthyroidism in pregnancy.

Can hyperthyroidism cause a false negative pregnancy test?

Several issues can lead to false negative or false positive results on a home pregnancy test. They can include:

  • medical conditions, such as thyroid issues
  • use of certain medications
  • taking the test too soon
  • dilution of the urine
  • user error

Also, according to a 2015 study, home pregnancy tests are often not nearly as accurate as they claim, which means the margin for error may be higher than advertised.

A person should follow up on any positive results with a doctor. They should also check with a doctor if they experience unusual symptoms and a negative test result.

Can pregnancy be mistaken for hyperthyroidism?

Symptoms of hyperthyroidism and early pregnancy are often similar and include increased heart rate and heat intolerance. Both states can also affect appetite and sleep cycles.

Therefore, a person may mistake their symptoms of hyperthyroidism for pregnancy. A person should speak with a doctor to confirm a diagnosis.

Can thyroid problems cause problems in pregnancy?

Thyroid issues can cause complications for both the pregnant person and the fetus.

Complications for the pregnant person can include:

  • gestational hypertension
  • preterm labor
  • increased risk of pregnancy loss
  • placental abruption
  • preeclampsia

Thyroid hormones play an essential role in fetal development, particularly in the early stages. Issues with the thyroid can cause issues to the fetus and newborn that can include:

  • low birth weight
  • prematurity
  • tachycardia
  • goiter
  • neurodevelopmental abnormalities
  • fetal hydrops
  • early bone maturation
  • cardiac failure
  • intrauterine growth restriction

Hyperthyroidism can occur during pregnancy. The most common cause is Graves’ disease, which causes inflammation of the thyroid.

Symptoms of hyperthyroidism can often mimic those a person experiences in early pregnancy. A person may not be able to distinguish between symptoms.

It is also possible for a person to experience elevated levels of thyroid hormones during early pregnancy that disappear during later pregnancy.

A person should consider talking with a doctor if they experience unusual symptoms or changes during pregnancy. With treatment, both the person and fetus can avoid potential complications and have a healthy delivery.