Congenital hypothyroidism: A newborn screening success story?

Congenital hypothyroidism, present in 1: 4000 newborns, is one of the most common preventable causes of mental retardation. Screening programs, now routine in all 50 states, Canada, and most of the developed world, have been immensely successful in detection and early treatment of affected infants. Diagnostic studies show thyroid dysgenesis to be the most common etiology worldwide, with ectopic glands accounting for the majority of dysgenetic cases. Other etiologies include hereditary defects in thyroxine synthesis, hypopituitary hypothyroidism, and transplacental passage of maternal thyrotropin receptor blocking antibodies; the latter condition is usually associated with transient hypothyroidism. Many programs report good psychometric outcomes, with IQs similar to control groups. Some, however, report slightly lower IQs, particularly in the most severely affected infants. These IQ differences may result from the effects of fetal hypothyroidism, neonatal hypothyroidism that occurs be assure proper dosing and compliance in the first 2 years is also important to neurologic outcome. The future may include screening of women of child-bearing age for hypothyroidism and some way to screen and treat the hypothyroid fetus.