Developmental follow-up of very low birthweight premature infants with low free thyroxine.

If a low level of free thyroxine (T4) is predictive of the true hypothyroidism in sick premature infants, long-term developmental follow-up of these infants should reveal a direct correlation between the free thyroxine level early in life and developmental disability in later years. Half of the 16 infants who were followed had normal free T4 (0.8 ng/dl or higher) and the remaining 8 infants had a low free T4 (0.38 +/- 0.15 ng/dl) during the first 2 weeks of life. Infants with low free T4 were followed sequentially during their stay in the neonatal intensive care unit and all eight showed free T4 levels more than 0.8 ng/dl by 36 to 44 weeks postconceptional age without any thyroid replacement. At follow-up, all 16 infants were functioning within normal range by Stanford-Binet testing at mean age of 4.6 years. There was no significant difference between the two groups in their motor development, hearing, language, or physical growth. Despite the small sample size, it appears there is no correlation between the free T4 levels during the first 2 weeks of life in infants 33 weeks' or less gestation and their developmental outcome at mean age of 4.6 years.