Related Experiment Videos
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.
Insights
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.
Objectives:
To supply normative data for screening thyroxine (T4) and thyrotropin concentrations correlated with birth weight and age at screening of infants with birth weights ranging from 400 to 5500 gm, and to document the effects of screening of very low birth weight (VLBW) infants, because VLBW infants comprise 0.86% of surviving newborn infants and have very low total T4 concentrations with normal or elevated free T4 concentrations as a result of deficient protein binding of thyroid hormones.
Study Design:
Both retrospective and prospective studies were used. We conducted retrospective analyses of screening of T4 and thyrotropin concentrations in 9,324 term, 18,946 low birth weight, and 3,450 VLBW infants in Massachusetts, and a prospective study of T4 and thyrotropin concentrations in 48 VLBW infants at 2 weeks of age. Forty of the infants also had hormone measurements at 4 weeks, 29 at 8 weeks of age, and 24 had analysis of cord blood samples.
Results:
Median T4 concentrations for each weight group (in 250 gm increments) increased progressively and significantly up to 2500 gm. Of the surviving VLBW infants, 1.5% had screening T4 concentrations that were unmeasurably low (<3.9 nmol/L (0.3 microgram/dl)). The mean T4 concentration varied with age at screening, increasing from cord blood concentrations to a peak at 1 to 3 days of age and thereafter decreasing to a nadir at about 2 weeks in both low birth weight and VLBW infants. In VLBW infants the mean concentrations return to the level of 1 to 3 days by 4 to 8 weeks of age. The incidence of screening thyrotropin concentrations > or = 40 mU/L correlates inversely with weight. The incidence of early, transient hypothyroidism in VLBW infants defined by this thyrotropin concentration was eight times that in term infants. Two infants had late-onset, transient hypothyroidism at 2 and 7 weeks, respectively.
Conclusions:
The normative data related to birth weight and age at screening allow proper interpretation of VLBW results for primary T4 and primary thyrotropin screening programs. Screening of the concentrations of T4 and thyrotropin in VLBW increases the number of secondary measurements of T4 in a primary thyrotropin screening program and the number of secondary thyrotropin measurements in a primary T4 screening program by 6% and 9%, respectively. We recommend screening analyses for VLBW infants in the latter part of the first week of life and again at 2 and 4 to 6 weeks of age. This protocol would increase the number of screening analyses by 1.6%.