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Thyroxine administration to infants of less than 30 weeks gestational age decreases plasma tri-iodothyronine
A G van Wassenaer1, J H Kok, F W Dekker
1Department of Neonatology, Academic Medical Center, University of Amsterdam, The Netherlands.
Insights
Thyroxine (T4) supplementation in very preterm infants prevents low T4 but lowers T3 levels. This suggests preterm infants may benefit from combined T4 and T3 hormone therapy.
Area of Science:
- Neonatal Endocrinology
- Pediatric Pharmacology
Background:
- Very preterm infants (<30 weeks gestation) often experience thyroid dysfunction.
- Thyroid hormone metabolism is critical for neurodevelopment in neonates.
Purpose of the Study:
- To evaluate the impact of thyroxine (T4) administration on thyroid hormone metabolism in very preterm infants.
- To determine if T4 supplementation affects levels of T4, T3, reverse T3 (rT3), and TSH.
Main Methods:
- A randomized, double-blind, placebo-controlled trial involving 200 infants (<30 weeks gestation).
- Infants received either T4 (8 microg/kg/day) or placebo from 12-24 hours after birth for 6 weeks.
- Weekly measurements of plasma T4, T3, rT3, TSH, and thyroxine-binding globulin.
Main Results:
- T4 and rT3 levels were significantly elevated in the T4 group.
- TSH concentrations were suppressed, and T3 levels were significantly decreased in infants receiving T4.
- Ratios of T4/T3 and T4/rT3 differed significantly between groups.
Conclusions:
- Daily T4 administration prevents hypothyroxinemia in very preterm infants but reduces plasma T3 concentrations.
- Findings suggest that very preterm infants might require supplementation with both T4 and T3.
Objective:
To investigate the effect on thyroid hormone metabolism of the administration of thyroxine to very preterm infants.
Design And Methods:
Two hundred infants of less than 30 weeks gestation were enrolled into a randomized, double-blind, placebo-controlled trial. Thyroxine (T4) (at a fixed daily dose of 8 microg/kg birthweight) or placebo was started 12-24h after birth and discontinued 6 weeks later. Plasma concentrations of T4, tri-iodothyronine (T3), reverse T3 (rT3), TSH, and thyroxine-binding globulin were measured weekly during trial medication and 2 weeks thereafter.
Results:
The T4 and the placebo group each comprised 100 infants. Antenatal, perinatal, and postnatal clinical characteristics were comparable in both groups. T4 and rT3 were significantly increased in the T4 group. TSH concentrations were depressed in the T4 group and T3 was significantly decreased, probably as a result of TSH depression. The T4/T3 and T4/rT3 ratios differed significantly between the two study groups.
Conclusions:
Daily T4 administration during the first 6 weeks after birth to infants of less than 30 weeks gestation prevents hypothyroxinemia, but decreases plasma T3 concentrations. Our finding possibly implies that very preterm infants should receive supplements of both T4 and T3.