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The relationship of insulin-like growth factor-I to total thyroxine in normal and low birth weight infants
M L Mitchell1, R J Hermos, M Feingold
1Massachusetts Department of Public Health, Newborn Screening Program, Jamaica Plain 02130.
Insights
Insulin-like Growth Factor-I (IGF-I) levels in newborns are influenced by birth weight and thyroxine levels. Higher IGF-I concentrations correlate with normal birth weight and adequate thyroxine, especially after the first week of life.
Area of Science:
- Pediatric Endocrinology
- Neonatal Metabolism
- Hormone Regulation
Background:
- Insulin-like Growth Factor-I (IGF-I) plays a crucial role in infant growth and development.
- Thyroxine is a key thyroid hormone essential for metabolic processes and growth.
- The interplay between IGF-I, birth weight, and thyroxine in neonates requires further elucidation.
Purpose of the Study:
- To investigate the relationship between IGF-I concentrations, birth weight, and thyroxine levels in newborns.
- To determine how these factors influence IGF-I levels during the early neonatal period.
Main Methods:
- Radioimmunoassay (RIA) was used to measure IGF-I concentrations in dried blood spots from infants aged 3-21 days.
- Infants were categorized by birth weight (normal >2.5 kg, low <2.5 kg) and thyroxine levels (normal >83.7 nmol/L, low <64.4 nmol/L).
Main Results:
- Infants with normal thyroxine levels had significantly higher mean IGF-I values than those with low thyroxine, irrespective of birth weight, during the first week of life.
- After the first week, infants with normal birth weight and normal thyroxine exhibited the highest IGF-I levels.
- Low birth weight infants with normal thyroxine showed a modest increase in IGF-I post-first week, surpassing those with low thyroxine.
Conclusions:
- IGF-I concentration is positively correlated with both total thyroxine levels and birth weight in neonates.
- Thyroxine levels appear to be a significant confounding factor when assessing the relationship between birth weight and IGF-I.
Abstract:
IGF-I concentrations were determined by RIA in eluates of dried blood collected on filter paper from infants who ranged in age from 3 to 21 d. The infants were separated into normal (greater than 2.5 kg) and low (less than 2.5 kg) birth wt groups and further subdivided on the basis of normal (greater than 83.7 nmol/liter) or low (less than 64.4 nmol/liter) levels of thyroxine. Both the normal and low birth wt groups whose blood thyroxine was in the normal range had similar mean IGF-I values during the 1st wk of life that were significantly higher (p less than 0.05) than those of either the normal or low birth wt groups whose thyroxine concentrations were below normal. Infants older than 1 wk of age with normal birth wt and normal thyroxine levels had significantly greater (p less than 0.05) mean IGF-I values than those of any of the other groups. Infants in the low birth wt-normal thyroxine group exhibited modest increases in IGF-I levels after the 1st wk of life that were significantly greater (p less than 0.05) than those found in the low birth wt-low thyroxine infants. These studies have demonstrated that IGF-I concentration is correlated positively with total thyroxine and with birth wt and that the latter is confounded by the former.