Congenital Hypothyroidism in Infants

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Newborn Infant in Mother's Arms, at Hospital
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Congenital hypothyroidism refers to a deficiency or lack of thyroid hormone that is present at birth. Genetic defects or maternal iodine deficiency can result in problems with thyroid gland development or with thyroid hormone production, giving rise to the condition. Usually, newborn screening tests identify congenital hypothyroidism. While babies do not typically have signs or symptoms of hypothyroidism at birth, there may be recognizable clues that parents can look for.

Congenital hypothyroidism affects about one out of every 4000 newborn babies and is considered among the most common and treatable causes of developmental delay worldwide. If your baby has congenital hypothyroidism, it is especially important that proper treatment is initiated early.

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 residual thyroid function.

Some signs and symptoms that your baby may have include:

  • 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 stomach
  • 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 (protruding) bellybutton
  • Little to no growth, failure to thrive

Causes

There are two main forms of congenital hypothyroidism: permanent congenital hypothyroidism and transient congenital hypothyroidism. Congenital hypothyroidism is more common in infants who have congenital heart problems or Down syndrome.

Permanent Congenital Hypothyroidism

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

  • Dysgenesis: This defect or abnormal development of the thyroid gland is the most common cause of congenital hypothyroidism, responsible for about two-thirds of cases. Ectopic (abnormally located) thyroid tissue is the most common defect.
  • A defect in the ability to synthesize and secrete thyroid hormone: This accounts for approximately 10 percent of cases of congenital hypothyroidism.
  • A defect in the thyroid hormone transport mechanism: This means that thyroid hormones may be produced, but do not have their intended effects on the body.
  • Central hypothyroidism: This is when the thyroid gland can make thyroid hormones but is not properly directed to do so by the hypothalamus or pituitary gland, both of which are located in the brain.

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:

  • Iodine deficiency: Iodine is needed to produce thyroid hormone. An iodine deficiency in a newborn results from insufficient iodine intake in the mother.
  • Antibodies: Thyroid stimulating hormone-receptor blocking antibodies (TRB-Ab) can develop in a pregnant woman with autoimmune thyroid disease, such as Graves' disease. The antibodies may travel across the placenta and interfere with the thyroid function of the growing baby, resulting in hypothyroidism at birth. This does not happen for all women with autoimmune thyroid disease. Typically, this type of congenital hypothyroidism resolves around age one to three months as the mother's antibodies are naturally cleared from the infant.
  • Medication exposure in utero: Antithyroid medications taken for treatment of hyperthyroidism can cross the placenta, causing hypothyroidism in the newborn. Usually, this type of hypothyroidism resolves several days after birth, and normal thyroid function returns within a few weeks.
  • Iodine exposure: Fetus or newborn exposure to very high doses of iodine 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) or use of iodine-containing antiseptics or contrast agents (used in diagnostic imaging tests).

    Diagnosis

    Congenital hypothyroidism is most often detected by newborn blood screening with a heel prick test that is done within a few days of birth. The routine test is usually followed up within two to six weeks after birth.

    Newborn screening for thyroid disease includes:

    • Thyroid stimulating hormone (TSH): Normal newborn range is 1.7 to 9.1 mU per L. High levels are suggestive of hypothyroidism.
    • Thyroxine (T4): Normal newborn range is 10 mcg per dL (129 nmol per L). Low levels are indicative of hypothyroidism.


    If the initial blood screening test identifies a potential problem, follow-up typically includes repeating the tests after about two to three weeks. Imaging tests for visualization of the thyroid gland are typically needed if thyroid blood tests remain abnormal. If there are other problems, such as heart defects or an unusual facial appearance, then additional diagnostic testing, such as electrocardiogram (EKG) to evaluate the heart or genetic tests, may be necessary.

    Treatment

    If a newborn is not treated for congenital hypothyroidism, this can negatively impact physical, cognitive, and neurological development. Along with management of the condition through use of medication, close follow-up of developmental milestones is also recommended.

    Medication

    Treatment with levothyroxine (L-thyroxine or L-T4) tablets or liquid is usually the preferred method of thyroid hormone replacement for infants. The dose, which is typically in the range of 8 mcg/kg/d to 10-15 mcg/kg/d, is calculated based on your baby's weight and response to the medication.

    The tablet can be crushed and given to your baby in his or her liquid formula for safe swallowing. The tablet and liquid form both have similar safety and therapeutic effects.

    Generally, thyroid hormone levels are expected to reach normal values within about 10 days after the initiation of treatment.

    Treatment will continue for as long as the condition is present.

    A Word from Verywell

    If you have a child born with congenital hypothyroidism, you can expect a good prognosis with normal growth and development if treatment is initiated early. It is also important that you discuss the cause of your child's congenital hypothyroidism with a pediatrician or genetic specialist. You may need to take precautions with your next pregnancies, such as maintaining an adequate iodine intake, or adjusting medication for your own thyroid condition with the supervision of your doctor.

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