Thyroid disorders occur if the thyroid gland produces too little thyroid hormone (hypothyroidism) or too much thyroid hormone (hyperthyroidism).
Hypothyroidism in the Newborn
The most common cause of hypothyroidism in the newborn is complete absence or underdevelopment of the thyroid gland. Less commonly, the thyroid gland is present but does not produce normal amounts of thyroid hormones.
Initially, the newborn may have no symptoms. Later, the newborn may become sluggish (lethargic) and have a poor appetite, low muscle tone, constipation, a hoarse cry, and a bulging of the abdominal contents at the bellybutton (an umbilical hernia). Untreated infants will have delayed development, intellectual disability, and short stature. Eventually, the infant may develop coarse facial features and an enlarged tongue.
Because early treatment can prevent intellectual disability, all newborns receive a screening blood test in the hospital after birth to evaluate thyroid function. In affected newborns, the blood test shows an elevated level of thyroid-stimulating hormone and usually a lower level of thyroid hormone. Many newborns with hypothyroidism require thyroid hormone given by mouth for their entire life. Treatment is directed by a doctor who specializes in treating children with problems of the endocrine system (a pediatric endocrinologist).
Hyperthyroidism in the Newborn
Rarely, a newborn may have hyperthyroidism, or neonatal Graves' disease. This condition usually 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: Autoimmune Disorders During Pregnancy), the mother's body produces antibodies that stimulate the thyroid gland to produce increased amounts of thyroid hormone. These antibodies cross the placenta and similarly affect the fetus.
An affected newborn has a high 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 at birth. A very rapid heart rate can lead to heart failure. Graves' disease is potentially fatal if not recognized and treated by a pediatric endocrinologist.
Doctors suspect hyperthyroidism based on the typical symptoms and confirm the diagnosis by detecting elevated levels of thyroid hormone and thyroid-stimulating antibodies from the mother in the newborn's blood. The results of a screening test of thyroid function done in all newborns may reveal hyperthyroidism.
Newborns with hyperthyroidism are treated with drugs, such as propylthiouracil, that slow the production of thyroid hormone by the thyroid gland. This treatment is needed only for a few months because the antibodies that cross the placenta from the mother eventually disappear from the infant's bloodstream.
Last full review/revision February 2009 by Arthur E. Kopelman, MD