Hypothyroidism in the newborn period

PURPOSE OF REVIEW: This review summarizes significant advances in the epidemiology, pathophysiology and treatment of congenital hypothyroidism, with a focus on thyroid dysfunction in preterm infants. RECENT FINDINGS: Congenital hypothyroidism appears to be increasing in incidence, primarily due to increased stringency of screening strategies, with smaller contributions from changing demographics and improved survival of increasingly premature infants. The greatest increase has been in mildly affected infants. Although many such cases are transient, some eventually prove to be severe and/or permanent. In preterm infants, transient hypothyroidism is common and may be delayed in onset. The cause is probably multifactorial, and inadequate iodine intake may contribute to some cases. Transient hypothyroxinemia of prematurity, also common in premature infants, is correlated with markers of inflammation. Despite concern about the potential morbidity of transient hypothyroxinemia of prematurity, the benefits and safety of treatment have not been established. Novel genetic causes of congenital hypothyroidism continue to be identified, and accumulating data support the sensitivity of infants with severe congenital hypothyroidism to small changes in levothyroxine formulation. SUMMARY: Changes in newborn screening strategies have increasingly identified thyroid function abnormalities of unclear clinical significance. Novel causes of congenital hypothyroidism continue to be identified, and new data continue to emerge regarding optimal therapy.