Changes in plasma thyroid hormone levels after a single dose of triiodothyronine in premature infants of less than 30 weeks gestational age.
OBJECTIVE
Evaluation of thyroid hormone response to a single administration of triiodothyronine (T3) early postnatally to premature infants of <30 weeks gestational age.


METHODS
A prospective clinical trial with historical control.


METHODS
Ten infants born <28 weeks gestational age and ten infants born between 28 and 30 weeks gestational age were given 0.5 microg/kg T3 intravenously at 12 h after birth. The infants <28 weeks gestational age were also treated with thyroxine (T4; 8 microg/kg, once daily) during the first 6 weeks of life. Premature infants from a previous trial served as a matched historical control group. Analysis of variance for repeated measurements was performed.


RESULTS
For the infants <28-30 weeks gestational age mean plasma T3 concentrations were significantly higher in the T3-treated group (P=0.027) for at least 2 weeks, whereas mean plasma levels of T4, free T4 and TSH were comparable. For the infants <28 weeks gestational age plasma T3 levels were also significantly different after correction for gestational age (P=0.0002), with either comparable or higher values in the T3-treated infants up to 56 days after injection of T3. Mean plasma free T4 levels were lower during the first 3 days and higher or comparable thereafter (P=0.0014), and TSH suppression was more evident in the T3-treated infants (P=0.003).


CONCLUSIONS
A single administration of T3 to premature infants <30 weeks gestational age early postnatally results in a sustained increase of plasma T3 levels during the first weeks of life. In infants of 28-30 weeks gestational age this occurs without change in plasma free T4 levels, whereas in infants <28 weeks gestational age a transient decrease of plasma free T4 was present. The increase in plasma T3 is possibly caused by a T3-induced increase of type I deiodinase activity.
Cools
F
F
Academic Hospital-Free University of Brussels, Dept Neonatology, Laarbeeklaan 101, 1090 Brussels, Belgium. Filip.Cools@az.vub.ac.be
van Wassenaer
A G
AG
Kok
J H
JH
de Vijlder
J J
JJ
D001794:Blood Pressure; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D005865:Gestational Age; D006339:Heart Rate; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood*; D019102:Infant, Very Low Birth Weight / Q000097:blood*; D008297:Male; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood* / Q000494:pharmacology*
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine