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Developmental follow-up of very low birthweight premature infants with low free thyroxine
1Department of Pediatrics, Michigan State University, East Lansing.
Insights
Early low free thyroxine (T4) levels in premature infants do not predict later developmental disabilities. Follow-up revealed no significant differences in development between infants with normal and low T4 levels.
Area of Science:
- Neonatal Medicine
- Endocrinology
- Developmental Pediatrics
Background:
- Low free thyroxine (T4) levels in sick premature infants may indicate hypothyroidism.
- Predictive value of early T4 for long-term neurodevelopmental outcomes requires investigation.
Purpose of the Study:
- To determine if early low free thyroxine (T4) levels in premature infants correlate with later developmental disabilities.
- To assess the neurodevelopmental outcomes of premature infants based on initial T4 levels.
Main Methods:
- Follow-up of 16 premature infants (gestation ≤33 weeks) with stratified analysis based on initial free T4 levels (normal vs. low).
- Sequential monitoring of free T4 levels during neonatal intensive care unit (NICU) stay.
- Neurodevelopmental assessment using Stanford-Binet testing at a mean age of 4.6 years.
Main Results:
- Half of the infants had normal initial free T4, while 8 had low levels.
- All infants with initially low free T4 normalized levels by 36-44 weeks postconceptional age without intervention.
- No significant differences were observed in motor development, hearing, language, or physical growth between the groups at follow-up.
Conclusions:
- Early low free thyroxine levels in premature infants (≤33 weeks gestation) do not appear to be predictive of developmental outcomes at 4.6 years.
- Further research with larger sample sizes is warranted to confirm these findings.
Abstract:
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.