Thyroxine values from newborn screening of 919 infants born before 29 weeks' gestation.

Abstract

Severe transient hypothyroxinemia in premature infants is associated with cerebral palsy and mental retardation: this study assessed its prevalence in very premature infants. Congenital hypothyroidism screening programs in three states provided thyroxine values for 919 newborn infants younger than 29 weeks who were enrolled in a multicenter study. Thyroxine values were lower than 4.0 micrograms/dL in 21% of survivors and increased each week by 0.6 microgram/dL (95% confidence interval [CI] = 0.4, 0.7). At tests done 1 to 2 days after birth, levels were 2.5 micrograms/dL higher (95% CI = 1.8, 3.3) than at tests done at 8 to 14 days. In New York, levels were 1.0 microgram/dL higher (95% CI = 0.3, 1.6) than elsewhere. The levels of infants who died were 1.3 micrograms/dL lower (95% CI = 0.6, 2.0) than those of survivors. Severe transient hypothyroxinemia is common in very premature infants and deserves further study.