Congenital hypothyroidism is a condition where the thyroid does not function properly from birth. If untreated, it can cause learning disabilities and neurological issues.

Congenital hypothyroidism (CH) is among the most common preventable causes of intellectual disability.

Early detection and treatment can help prevent complications.

This article reviews CH and its symptoms, causes, risk factors, and more.

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Congenital hypothyroidism occurs when the thyroid does not function properly. This causes a lack of thyroid hormones thyroxine (T4) and triiodothyronine (T3).

These hormones play an important part in brain development and growth. With early screening and detection, doctors can treat the condition and allow for normal growth and brain development.

Without treatment, the lack of hormones can lead to intellectual disability and other health concerns.

The condition affects between 1 in 3,000–4,000 live births worldwide. It is also more common in Hispanic and Asian babies and less frequent in Black infants.

It is also between 1.5–2 times more likely to occur in females.

Learn more about common thyroid disorders.

Doctors screen for congenital hypothyroidism at birth in the United States. This helps to identify it sooner, which can help with treatment.

Another reason for screening is that newborns may not show any signs or symptoms related to the condition.

If they do occur, they may appear at birth or develop over the course of a few months.

In infants, symptoms may include:

  • constipation
  • puffy-looking face
  • hypotonia (low muscle tone)
  • large soft spots on the skull
  • hoarse cry
  • jaundice (yellowing of skin and eyes)
  • large, thick tongue
  • distended stomach with umbilical hernia
  • feeding issues, such as needing to be awakened for feeding time

This section looks at the possible causes of congenital hypothyroidism.

Thyroid gland abnormalities

An abnormality in thyroid gland development (thyroid dysgenesis) causes about 80% of CH cases.

Thyroid dysgenesis mostly happens sporadically, and a person does not usually inherit it from their parents.

However, in 2–5% of cases, a mutation in the genes responsible for thyroid development can cause CH. These genes are:

  • PAX8
  • NKX2-1
  • FOXE1

Types of thyroid dysgenesis include:

  • Ectopic thyroid gland: a gland that develops in an abnormal position
  • Thyroid hypoplasia: an underdeveloped thyroid gland
  • Thyroid agenesis: a missing thyroid gland

Thyroid hormone imbalances

Although thyroid dysgenesis is the main cause, a thyroid hormone imbalance (dyshormonogenesis) can also cause CH.

If an infant has dyshormonogenesis, their future siblings have a 1 in 4 chance of developing dyshormonogenesis as well.

Temporary causes

The above conditions cause permanent CH, but the condition can also happen temporarily.

Possible causes of temporary congenital hypothyroidism include:

  • exposure to too much or too little iodine in the womb
  • the parent’s antithyroid medications (methimazole or propylthiouracil) passing to the fetus during pregnancy
  • a parent with an autoimmune thyroid disease passing thyroid-blocking antibodies to the fetus during pregnancy

The main cause of congenital hypothyroidism — thyroid dysgenesis — typically occurs spontaneously and is unpredictable. A sibling is not likely to develop the condition.

Having dyshormonogenesis is another risk factor for CH. A person can inherit dyshormonogenesis if both of their parents are carriers of the disease.

If both parents are carriers, there is a 1 in 4 chance that an offspring will have the disorder. One parent cannot pass on the disorder.

Risk factors for giving birth to a child with temporary CH can include:

  • having Hashimoto’s thyroiditis, as the parent may pass on thyroid-blocking antibodies
  • taking medications to treat hypothyroidism during pregnancy
  • taking high amounts of iodine during pregnancy
  • not having enough iodine during pregnancy

However, temporary CH may only last for a few weeks or months.

In the United States, doctors typically test for congenital hypothyroidism within 1–2 days of birth.

The doctor will perform a heel prick to collect a few small drops of blood from the baby. They will send the sample to a lab for testing.

The lab looks for the presence of:

  • TSH (thyroid stimulating hormone)
  • T4 (thyroxine)

The lab sends the results to the primary care doctor or hospital. Low T4 levels combined with elevated TSH levels suggest CH.

To confirm, a doctor may need to pull blood directly from a vein and repeat the screening.

A doctor can confirm the diagnosis if similar results come back.

Treatment typically requires a doctor to replace the thyroid hormones the body normally produces.

A common first-line treatment involves the use of levothyroxine. Levothyroxine is a synthetic form of T4, which the thyroid would ordinarily produce.

Doctors will typically start treatment immediately upon diagnosis. Dosing will vary based on the severity of the condition, but often a doctor will start at 10–15 micrograms (mg) per day for more severe cases.

When treatment starts between 1–2 weeks of life, the baby has a lower chance of developing intellectual disabilities.

After 1–2 weeks of treatment, a doctor will likely recommend a follow-up test to check the baby’s levels. They will then recommend testing once every 1–3 months for the first year of life.

Once the baby has reached 1 year of life, screening will repeat once every 2–4 months until around the age of 3 years.

After that age, they will need screening once every 3–12 months until they have stopped growing.

The number of times a child may need screening will vary based on factors such as response to treatment. A person should follow a doctor’s recommended follow-up schedule.

A baby can experience impaired cognitive development if they do not receive treatment for CH or if treatment starts later in life.

This can result in learning disabilities and issues with coordination later in life.

Treatment should start within 1–2 weeks of life to decrease the risk of long-term complications.

Congenital hypothyroidism may be temporary or lifelong. Temporary cases may clear within a few weeks or months.

Children with lifelong CH will need regular doses of levothyroxine. The parent will need to speak to a doctor about dosing and follow-up testing.

After the age of 3 years — when the critical brain development phase is over — a doctor may recommend stopping treatment and then testing levels. If they come back normal, the child may no longer need treatment for the condition.

In either case, a person can live an otherwise normal life with regular treatment and testing.

The majority of cases of congenital hypothyroidism occur due to a spontaneous mutation. Most cases are non-inherited. This means it is not possible to prevent most cases.

However, some cases of CH can result from dyshormonogenesis, an inherited condition. Two parents that are carriers of the disease can pass it on to a child, but they may not be aware they are carriers.

If a couple has a child with dyshormonogenesis, there is a 1 in 4 chance that their future siblings will also have the disorder. Parents who already have a child with dyshormonogenesis may want to consider their chances of passing it on to another child.

Taking certain medications for thyroid problems during pregnancy can cause temporary CH, though this is less common.

A person should talk with a doctor about taking medications during pregnancy or if they are trying to conceive. They may have to review their thyroid medications to prevent CH.

Congenital hypothyroidism is not very common, affecting between 1 in 3,000–4,000 births.

Specific organizations dedicated to congenital hypothyroidism are also not common. However, a person can visit the American Thyroid Association for information, the latest research, resources, and more.

A person can also ask a doctor or hospital for information on local organizations that may provide support and help with paying for doctor visits or medications.

Pharmacies also tend to offer discount programs and coupons for people with or without insurance who may have trouble paying for their medication.

The following section provides answers to frequently asked questions about congenital hypothyroidism.

What is the most common cause of congenital hypothyroidism?

The cause of about 80% of congenital hypothyroidism is thyroid dysgenesis, where the thyroid does not develop normally.

This occurs spontaneously and is non-inherited, which means there is nothing a parent can do to prevent it from happening.

How serious is congenital hypothyroidism?

Left untreated or undiscovered, congenital hypothyroidism can lead to intellectual disability, learning difficulties, and other cognitive issues.

Starting treatment within 1–2 weeks of life can help significantly improve a child’s chances of developing normally.

Is congenital hypothyroidism genetic?

Most cases of congenital hypothyroidism are genetic but nonhereditary. Instead, the mutation occurs randomly during development. This means that most cases are not due to a parent passing down the gene.

However, a less common cause of CH — dyshormonogenesis — can be hereditary. If two parents are carriers of the disease, they can pass it on to a child.

If a child has dyshormonogenesis, there is a 1 in 4 chance that their future siblings will also have the disorder.

Congenital hypothyroidism occurs when the thyroid does not develop properly or produce enough thyroid hormone.

The majority of cases are spontaneous genetic developments. However, it is possible to pass CH-causing genes to a child.

Compilations include learning disabilities and long-term cognitive difficulties.

Screening in the first 2 days of life and early treatment can help prevent more serious complications.

Treatment may be temporary if the condition is transient, but many will need lifelong treatment.