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Hypothyroidism in the Newborn

By

Andrew Calabria

, MD, Perelman School of Medicine at The University of Pennsylvania

Last full review/revision Sep 2020| Content last modified Sep 2020
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Hypothyroidism is decreased production of thyroid hormone.

  • Hypothyroidism in the newborn may occur if there is a structural problem with the thyroid gland.

  • Symptoms may include delayed growth and development over time.

  • The diagnosis is based on newborn screening tests, thyroid function tests, and scanning tests.

  • Treatment includes giving thyroid hormone replacement.

The thyroid gland secretes thyroid hormone. Thyroid hormone controls the speed of the body's metabolism, including how fast the heart beats and how the body regulates temperature. If the thyroid gland does not produce enough thyroid hormone, these functions slow down.

Hypothyroidism that is present at birth is called congenital hypothyroidism. Congenital hypothyroidism occurs in about 1 in 2,000 to 3,000 births. Most cases occur spontaneously, but about 10 to 20% are inherited.

The most common cause of hypothyroidism in the newborn is

  • Complete absence of the thyroid gland, underdevelopment of the thyroid gland, or development in the wrong place

Less commonly, the thyroid gland is present but does not produce normal amounts of thyroid hormones. In certain developing countries, hypothyroidism occurs when the mother has an iodine deficiency. Rarely, certain antibodies of the mother or drugs that cause enlargement of the thyroid gland or antithyroid drugs taken by the mother cross the placenta and cause temporary hypothyroidism in the newborn. In another rare cause, the pituitary gland is abnormally formed and fails to stimulate the thyroid gland to produce thyroid hormones (central hypothyroidism).

Symptoms

Initially, the newborn may have no symptoms of hypothyroidism. Later, if the underlying cause of hypothyroidism is not identified and hypothyroidism remains undiagnosed or untreated, development of the central nervous system is slowed. The newborn may become sluggish (lethargic) and have a poor appetite, yellowing of the skin (jaundice), low muscle tone, constipation, large fontanelles, a hoarse cry, low heart rate, and a bulging of the abdominal contents at the bellybutton (called an umbilical hernia). If the newborn has an enlarged thyroid gland (congenital goiter), the gland may press against the windpipe and interfere with breathing at birth. A delay in the diagnosis and treatment of severe hypothyroidism causes intellectual disability and short stature. Eventually, the infant may develop dry, cool, mottled skin, coarse facial features (such as a flat, broad nasal bridge and a puffy face), and a slightly open mouth with an enlarged tongue.

Diagnosis

  • Newborn screening test

  • Thyroid function tests

  • Imaging tests

Because early treatment can prevent intellectual disability, all newborns receive a routine screening blood test in the hospital after birth to evaluate thyroid function.

If the result of the screening test is positive, thyroid function tests, which are blood tests, are done. In affected newborns, the blood test shows an elevated level of thyroid-stimulating hormone and usually a lower level of thyroid hormone.

After hypothyroidism of the newborn is diagnosed, doctors do imaging tests to evaluate the size and location of the thyroid gland. These tests include radionuclide scanning or ultrasonography.

Doctors do magnetic resonance imaging (MRI) of the brain and pituitary gland in children who have central hypothyroidism to rule out problems in the brain.

Prognosis

Most infants who are treated have normal movement control and intellectual development.

Even when treated promptly, severe congenital hypothyroidism may still cause subtle developmental problems and hearing loss. Hearing loss may be so mild that it is not detected during the routine newborn screening but it may still interfere with language learning. To detect subtle hearing loss, infants are tested again when they are older.

Treatment

  • Thyroid hormone replacement

Most newborns with hypothyroidism are given the synthetic thyroid hormone levothyroxine by mouth. It should not be given simultaneously with soy formula, or iron or calcium supplements because these substances can decrease the amount of levothyroxine that is absorbed. Most children who have congenital hypothyroidism need to take thyroid hormone replacement for their entire life. However, some children, usually those who have not required a dose increase after infancy, may be able to stop treatment after they are about 3 years of age. Treatment of hypothyroidism is directed by a doctor who specializes in treating children with problems of the endocrine system (called a pediatric endocrinologist).

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