Congenital Hypothyroidism in Infants and Children

Newborn Infant in Mother's Arms, at Hospital
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Congenital hypothyroidism refers to hypothyroidism — a deficiency or lack of thyroid hormone — at birth.

In the era of newborn screening, congenital hypothyroidism is extremely rare. Still, if present, it is especially important that it be diagnosed quickly and properly treated. Failing to properly and promptly treat congenital hypothyroidism can negatively affect IQ and neurological development. Congenital hypothyroidism is actually one of the most common yet treatable causes of mental retardation worldwide.

There are two main forms of congenital hypothyroidism: permanent congenital hypothyroidism and transient congenital hypothyroidism.

Permanent Congenital Hypothyroidism

This sort of hypothyroidism requires lifelong treatment, and has a number of causes:

  • The most common cause of congenital hypothyroidism is a defect or abnormal development of the thyroid gland, known as dysgenesis. In particular, abnormally located (ectopic) thyroid tissue is the most common defect. Approximately two-thirds of congenital hypothyroidism is a result of dysgenesis.
  • Some infants inherit defects in the ability to synthesize and secret thyroid hormone. These account for approximately 10 percent of cases of congenital hypothyroidism.
  • Congenital hypothyroidism can be due to a defect in the thyroid hormone transport mechanism.
  • In some infants, central hypothyroidism, which involves hypothalamic or pituitary problems,is the cause of congenital hypothyroidism.

Transient Congenital Hypothyroidism

It's thought that 10 to 20 percent of newborns who are hypothyroid have a temporary form of the condition known as transient congenital hypothyroidism. Transient hypothyroidism in newborns has several causes:

  • An iodine deficiency in the newborn, which results from insufficient iodine intake in the mother
  • TSH-receptor blocking antibodies (TRB-Ab) in a pregnant woman with autoimmune thyroid disease, usually Graves' disease, transferring across the placenta and affecting thyroid function of the fetus, causing hypothyroidism at birth. This does not happen in all women with autoimmune thyroid disease. Typically, when it does, the hypothyroidism resolves around one to three months after birth as the mother's antibodies are naturally cleared from the infant.
  • Antithyroid drugs (PTU, methimazole) taken by a pregnant woman who is hyperthyroid crossing the placenta, causing hypothyroidism in the newborn. Usually, the hypothyroidism resolves several days after birth, and normal thyroid function returns within a few weeks.
  • Fetus or newborn exposure to very high doses of iodine, which can cause transient hypothyroidism. This sort of iodine exposure results from use of an iodine-based medication like amiodarone (used to treat irregular heart rhythms) in mother or baby, or use of iodine-containing antiseptics or contrast agents.

    Signs and Symptoms 

    Most newborns with congenital hypothyroidism do not have any signs or symptoms of the condition. This is due to the presence of some maternal thyroid hormone, or some residual thyroid function of their own.

    But, clinical signs and symptoms can include the following:

    • Increased birth weight
    • Increased head circumference
    • Lethargy (lack of energy, sleeps most of the time, appears tired even when awake)
    • Slow movement
    • A hoarse cry
    • Feeding problems
    • Persistent constipation, bloated or full to the touch
    • An enlarged tongue
    • Dry skin
    • Low body temperature
    • Prolonged jaundice
    • A goiter (enlarged thyroid)
    • Abnormally low muscle tone
    • Puffy face
    • Cold extremities
    • Thick coarse hair that goes low on the forehead
    • A large fontanel (soft spot)
    • A herniated bellybutton
    • Little to no growth, failure to thrive

    Congenital hypothyroidism is more common in infants who have other congenital malformations (mostly heart-related) and Down syndrome.

    Detection and Diagnosis 

    Congenital hypothyroidism is most often detected by screening of newborns, usually accomplished by a heel prick test done within a few days of birth. The test is usually followed up within two to six weeks after birth.

    According to medical reference UpToDate:

    "Screening of all newborns is now routine in all 50 states of the United States, Canada, Europe, Israel, Japan, Australia and New Zealand, and is under development in Eastern Europe, South America, Asia, and Africa. In the United States, for example, more than 4 million infants are screened annually, leading to the detection of 1000 infants with congenital hypothyroidism. Worldwide, it is estimated 12 million infants are screened and 3,000 with hypothyroidism are detected annually."

    When the initial blood screening test identifies a potential problem, follow-up typically includes additional blood work and may include other tests, such as thyroid imaging tests. UpToDate has extensive details regarding the various diagnostic procedures used to confirm congenital hypothyroidism and assess its causes.

    A Word from Verywell

    If you have a child born with congenital hypothyroidism, what is his or her prognosis? If your child's condition is detected at birth and treated quickly, the prognosis is excellent. According to research, children detected at birth who receive early treatment typically have normal growth and development, and most studies report no difference in IQ.

    Some studies, however, have found a slight reduction in verbal, math, and IQ scores, as well as slight deficits in memory and attention in some children restored to normal thyroid levels more slowly, due to delayed diagnosis or lower starting doses. Early and sufficient treatment for congenital hypothyroidism is, therefore, especially important.


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