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Thyroid function in very low birth weight infants: effects on neonatal hypothyroidism screening
J E Frank1, J E Faix, R J Hermos
1Department of Pediatrics, Dartmouth Medical School, Lebanon, NH 03756, USA.
The Journal of Pediatrics
|April 1, 1996
Summary
This study provides crucial normative data for screening thyroxine (T4) and thyrotropin in newborns. It highlights the need for tailored screening protocols for very low birth weight (VLBW) infants to accurately interpret thyroid hormone levels.
Area of Science:
- Endocrinology
- Neonatal Medicine
- Pediatric Screening
Background:
- Very low birth weight (VLBW) infants exhibit unique patterns in thyroid hormone levels due to altered protein binding.
- Standard newborn screening protocols may not adequately capture thyroid dysfunction in VLBW infants.
Purpose of the Study:
- To establish normative data for thyroxine (T4) and thyrotropin screening based on birth weight and age.
- To document the impact of screening on VLBW infants and refine diagnostic approaches.
Main Methods:
- Retrospective analysis of T4 and thyrotropin screening data from 9,324 term, 18,946 low birth weight, and 3,450 VLBW infants.
- Prospective study involving T4 and thyrotropin measurements in 48 VLBW infants at 2, 4, and 8 weeks of age, including cord blood analysis.
Main Results:
- Median T4 concentrations increased with birth weight up to 2500 gm.
- 1.5% of VLBW infants had unmeasurably low T4 levels.
- Thyrotropin levels > or = 40 mU/L were inversely correlated with weight, with VLBW infants showing an eightfold higher incidence of transient hypothyroidism.
Conclusions:
- Normative data aid in interpreting VLBW infant screening results for T4 and thyrotropin.
- Screening VLBW infants requires adjustments to primary screening programs, increasing secondary measurements.
- Recommended screening at the end of the first week, and at 2 and 4-6 weeks of age for VLBW infants.