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

OBJECTIVES: Severe transient hypothyroxinemia in premature infants is associated with cerebral palsy and mental retardation: this study assessed its prevalence in very premature infants. METHODS: 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. RESULTS: 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. CONCLUSIONS: Severe transient hypothyroxinemia is common in very premature infants and deserves further study.