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Frequency of transient hypothyroxinaemia in low birthweight infants. Potential pitfall for neonatal screening
Insights
Transient hypothyroxinemia is common in low birthweight infants, especially those with hyaline membrane disease or small-for-gestational-age. This transient condition requires careful consideration during congenital hypothyroidism screening.
Area of Science:
- Neonatal endocrinology
- Pediatric thyroid disorders
Background:
- Low birthweight infants are a vulnerable population.
- Thyroid hormone plays a crucial role in infant development.
Purpose of the Study:
- To investigate thyroid function in low birthweight infants.
- To identify factors associated with abnormal thyroid hormone levels.
Main Methods:
- Studied thyroid function in 54 low birthweight infants over 3 weeks.
- Categorized infants into three groups: well, with hyaline membrane disease, and small-for-gestational-age.
- Measured serum thyroxine and thyrotropin levels, and T3-charcoal uptake.
Main Results:
- A high incidence of transient hypothyroxinemia (low serum thyroxine) was observed.
- Infants with hyaline membrane disease and small-for-gestational-age infants showed higher rates of hypothyroxinemia.
- Serum thyrotropin levels and thyroid hormone binding remained normal.
Conclusions:
- Transient hypothyroxinemia is prevalent in low birthweight infants.
- Hyaline membrane disease and being small-for-gestational-age are associated with increased risk.
- Combined thyroxine and thyrotropin testing is recommended for congenital hypothyroidism screening in this population.
Abstract:
Thyroid function was studied in 54 low birthweight infants during a 3-week period. Each infant was placed in one of three groups. Group 1 (n = 21), infants who were well and appropriately grown fro gestational age; group 2 (n = 23), infants who were appropriately grown but who had hyaline membrane disease; group 3 (n = 10), infants who were small-for-gestational-age. In group 1, 5 (24%) infants had at least one serum thyroxine value less than 3.0 micrograms/100 ml (39 nmol/l). There were 8 (35%) infants in group 2 who had similarly low serum thyroxine values as did 5 (50%) of the 10 infants in group 3. Serum thyrotropin levels and serum binding of the thyroid hormones, as measured by a T3-charcoal uptake test, were normal in all infants. In all instances but 2, serum thyroxine values were at least 4.0 micrograms/100 ml (51 nmol/l) by the end of the 3-week period. There is thus a high incidence of transient 'hypothyroxinaemia' in low birthweight infants, particularly if such infants have hyaline membrane disease or are small-for-gestational-age. These findings must be considered when interpreting results of screening programmes for congenital hypothyroidism and they lend further support to the use of a combination of serum thyroxine and thyrotropin determinations for optimum screening of such infants.