Growth-restricted premature infants are at increased risk for low thyroxine.
OBJECTIVE
To evaluate, in extremely premature infants, the relationship between growth restriction and early total thyroxine levels, and to determine how maternal, prenatal, perinatal and neonatal variables influence the relationship.


METHODS
719 infants born at four medical centers in Massachusetts, New York and New Jersey between 1991 and 1993 were studied. Entry criteria included: gestational age 23--30 weeks, birth weight 500--1500 g, and a serum thyroxine level obtained in the first week of life. Infants born to mothers with a history of thyroid disease were excluded. Birth weight and total thyroxine level are expressed as z-scores (standard deviation units) to adjust for their relationship to gestational age.


RESULTS
In linear regression analysis, there was a 0.18 decrease in the total thyroxine z-score for each 1.0 (1 standard deviation unit) decrease in birth weight z-score (p=0.0001). Adjustment for multiple potential maternal, prenatal, perinatal and neonatal confounders failed to identify a factor or factors that could account for the observed association.


CONCLUSIONS
The early total thyroxine level in extremely preterm infants was significantly associated with birth weight z-score. This relationship persisted even after adjustment for maternal, prenatal, perinatal and neonatal confounders suggesting antenatal influences. Of clinical importance, growth-restricted infants are at increased risk for early hypothyroxinemia and, possibly, to its related morbidities.
Martin
C R
CR
Department of Neonatology, Beth Israel Deaconess Medical Center, Division of Newborn Medicine, Boston, MA, USA. cmartin1@caregroup.harvard.edu
Van Marter
L J
LJ
Allred
E N
EN
Leviton
A
A
D000328:Adult; D001724:Birth Weight; D005260:Female; D005317:Fetal Growth Retardation / Q000097:blood*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood*; D019102:Infant, Very Low Birth Weight / Q000097:blood*; D016014:Linear Models; D015997:Neonatal Screening; D013974:Thyroxine / Q000097:blood* / Q000172:deficiency
D013974:Thyroxine