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Maturation of feedback control of thyrotropin in premature infants
Insights
Thyroid hormone regulation in preterm infants shows delayed maturation of pituitary TSH feedback control after 6 weeks. This developmental pattern mirrors that of the intrauterine fetus, indicating a similar thyroid maturation process.
Area of Science:
- Neonatal Medicine
- Endocrinology
- Pediatric Physiology
Background:
- Preterm infants exhibit unique physiological challenges, including potential thyroid dysfunction.
- Understanding the maturation of the hypothalamic-pituitary-thyroid (HPT) axis is crucial for neonatal care.
Purpose of the Study:
- To longitudinally assess thyroid hormone levels and feedback mechanisms in preterm infants.
- To determine the postnatal maturation timeline of the HPT axis in extremely premature neonates.
Main Methods:
- Longitudinal measurement of serum thyrotropin (TSH), free T4, and free T3 in 26 preterm infants over 14 weeks.
- Utilized highly sensitive immunoradiometric assays for accurate hormone quantification.
Main Results:
- Serum TSH levels correlated positively with gestational age and birth weight in early postnatal life.
- TSH concentrations peaked around 5 weeks, with free T3 reaching term infant ranges by 6 weeks.
- Thyroid hormone feedback control maturation was observed after 6 weeks of postnatal age.
Conclusions:
- The HPT axis in extremely preterm infants demonstrates delayed maturation of TSH feedback control post-6 weeks.
- The observed maturation pattern suggests similarities between preterm infants and intrauterine fetuses regarding thyroid development.
Abstract:
Serum thyrotropin (TSH), free T4 and free T3 concentrations were measured longitudinally in 26 preterm infants for 14 weeks after birth, using highly sensitive immunoradiometric assays. Serum TSH values on days 4-5 were positively correlated with gestational age and birth weight. In the premature infants of 25 weeks mean gestation, the mean TSH concentrations increased from a very low value of 0.84 microU/ml at 5 days to a peak value of 6.1 microU/ml by 5 weeks of age, then slightly decreased and remained stable. Serum free T4 and free T3 concentrations increased in parallel and free T3 level reached the range of term infants by 6 weeks. Serum free T4/TSH and free T3/TSH ratios began to increase at the 6th week of age. The results suggest that: (i) the thyroid hormone feedback control of pituitary TSH release in the extremely premature infants begins to mature after 6 weeks of postnatal age, (ii) the maturation pattern of the hypothalamic-pituitary-thyroid system in premature infants is similar to that of the intrauterine fetus.