Risk factors associated with delayed thyrotropin elevations in congenital hypothyroidism

OBJECTIVES: To identify risk factors associated with delayed thyrotropin elevations in cases of congenital hypothyroidism. To determine whether routine rescreening of babies who have very low birth weight (VLBW) and babies in the neonatal intensive care unit is justified. STUDY DESIGN: Retrospective review of the New England Newborn Screening database (January 1989-June 2002) of newborns screened for hypothyroidism to determine the incidence of congenital hypothyroidism associated with delayed thyrotropin elevations and to characterize features associated with delayed thyrotropin elevations in newborns with VLBW and non-VLBW (NVLBW). RESULTS: The incidence of hypothyroidism was 14-fold higher for newborns with VLBW (1:250) compared with newborns with NVLBW (1:3500). Of the newborns with VLBW, two thirds were not detectable on the initial screening specimen. Among newborns with VLBW with delayed thyrotropin elevation, iodine exposure was found in 23%. Among newborns with NVLBW, 45% had congenital cardiac anomalies. For every 20 NVLBW cases of congenital hypothyroidism detectable by initial screening specimen, one additional case was detected with delayed thyrotropin elevation. CONCLUSIONS: Routine rescreening of babies with VLBW and babies in the neonatal intensive care unit is justified, and particular attention to follow-up testing of newborns known to have cardiac disease is warranted.