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Pituitary-thyroid responsiveness to thyrotropin-releasing hormone in preterm and small-for-gestational age newborns
Insights
Thyrotropin-releasing hormone (TRH) testing in preterm and small-for-gestational age newborns shows a pituitary TSH response similar to fullterm infants, but less pronounced later in infancy.
Area of Science:
- Neonatal endocrinology
- Pediatric endocrinology
- Thyroid function testing
Background:
- Premature and small-for-gestational age infants may have altered endocrine development.
- Thyroid hormone plays a critical role in neonatal development and metabolism.
- Understanding the pituitary-thyroid axis response in these vulnerable populations is crucial.
Purpose of the Study:
- To evaluate the pituitary-thyroid axis response to thyrotropin-releasing hormone (TRH) in preterm (PT) and small-for-gestational age (SGA) newborns.
- To compare the TSH and thyroid hormone response in PT and SGA infants with fullterm newborns and later infancy.
- To investigate potential correlations between basal TSH and TSH response in these neonatal groups.
Main Methods:
- Intravenous injection of 40 micrograms TRH in 12 PT and 15 SGA infants within 167 hours of birth.
- Measurement of serum TSH at baseline, 30, and 180 minutes post-TRH.
- Measurement of serum T4 and T3 at baseline and 180 minutes post-TRH.
Main Results:
- Pituitary TSH response to TRH in PT and SGA infants was comparable to fullterm newborns.
- SGA infants showed a significant correlation between serum TSH at 30 minutes and basal TSH levels.
- Thyroid hormone (T3 and T4) increases post-TRH were similar in PT and SGA groups, comparable to fullterms and adults.
Conclusions:
- The pituitary TSH response to exogenous TRH in low-birth-weight newborns is similar to fullterm infants and more pronounced than later in infancy.
- The thyroid hormone response to TRH is of similar magnitude in PT and SGA newborns as observed in fullterm infants and adults.
- These findings suggest a mature pituitary-thyroid axis response in PT and SGA neonates, though TSH response may diminish with age.
Abstract:
A dose of 40 microgram TRH was injected intravenously in 12 preterm (PT) and 15 small-for-gestational age (SGA) babies (with advanced gestational ages) between 5 and 167 hours after birth. Serum-thyrotropin (TSH) was measured prior to and 30 and 180 min after TRH; serum-thyroxine (T4) and serum-triiodothyronine (T3) were measured prior to and 180 min after TRH. The percentage increase in serum-TSH in PT and SGA babies was comparable to that of fullterm newborns. The serum-TSH 30 min after TRH in SGA newborns was significantly correlated to basal TSH values, such a correlation could not be shown in the preterms. One SGA and four PT babies had a repeat TRH-test performed later in infancy: In all but one PT with a gestational age of 27 weeks the TSH rise was lower than in the neonatal period. The thyroid hormone responses after TRH were similar in the two groups of babies. The percentage increase above basal levels were: Median serum-T3 increase about 46% and median serum-T4 increase about 14%. It is concluded that in low-birth-weight newborn babies the pituitary TSH response to exogenous TRH was like that detected in fullterm newborns and more pronounced that later in infancy. The effect of endogenous TSH as measured by thyroid hormone increases was of the same magnitude as observed in fullterms and in adults.