Diseases & Conditions
These disorders occur if the thyroid gland produces too little thyroid hormone (hypothyroidism) or too much thyroid hormone (hyperthyroidism).
Hypothyroidism: If untreated, hypothyroidism in the newborn results in poor growth and mental delay, eventually resulting in mental retardation. The most common cause of hypothyroidism in the newborn is complete absence or underdevelopment of the thyroid gland. Initially, the newborn has no symptoms. Later, the newborn may have lethargy, poor appetite, constipation, a hoarse cry, umbilical hernia (a bulging of the abdominal contents where the umbilicus penetrates the abdominal wall), and slow growth. Eventually, the infant may develop coarse facial features and an enlarged tongue.
Early treatment can prevent mental retardation. For this reason, a blood test is performed in the hospital after birth on all newborns to measure thyroid hormone levels. Treatment is with thyroid hormone.
Hyperthyroidism: Rarely, a newborn may have hyperthyroidism, or neonatal Graves' disease. This generally occurs if the mother has Graves' disease during pregnancy or has been treated for it before pregnancy. In Graves' disease (see Pregnancy Complicated by Disease: Graves' Disease ), the woman's body produces antibodies that stimulate the thyroid gland to produce increased blood levels of thyroid hormone. These antibodies cross the placenta and similarly affect the fetus. The result in an affected newborn is too high a metabolic rate, with rapid heart rate and breathing, irritability, and excessive appetite with poor weight gain.
The newborn, like the mother, may have bulging eyes (exophthalmos). If the newborn has an enlarged thyroid gland (goiter), the gland may press against the windpipe and interfere with breathing. A very rapid heart rate can lead to heart failure. Graves' disease is potentially fatal if not recognized and treated.
Doctors suspect hyperthyroidism by the typical symptoms and confirm the diagnosis by measuring elevated levels of thyroid hormone and the thyroid-stimulating antibodies from the mother in the newborn's blood.
Newborns with hyperthyroidism are treated with drugs, such as propylthiouracil, that slow the production of thyroid hormone by the thyroid gland. Treatment is needed for only a few months because the antibodies that cross the placenta from the mother only last in the infant's bloodstream for this long.
Last full review/revision February 2003
Source: The Merck Manual Home Edition