Growth-restricted premature infants are at increased risk for low thyroxine

• Published in: Early human development Vol. 64; no. 2; pp. 119 - 128
• Main Authors: Martin, Camilia R, Van Marter, Linda J, Allred, Elizabeth N, Leviton, Alan
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier Ireland Ltd 01-09-2001; New York,NY Elsevier; Amsterdam
• Subjects: Adult; Biological and medical sciences; Birth Weight; Diseases of mother, fetus and pregnancy; Female; Fetal Growth Retardation - blood; Gestational Age; Gynecology. Andrology. Obstetrics; Humans; Hypothyroidism; Infant, Newborn; Infant, Premature - blood; Infant, Very Low Birth Weight - blood; Intrauterine growth restriction; Linear Models; Low birth weight; Medical sciences; Neonatal Screening; Pregnancy. Fetus. Placenta; Premature newborn; Thyroid; Thyroxine - blood; Thyroxine - deficiency; Intrauterine growth restriction; Premature newborn; Hypothyroidism; Low birth weight; Thyroid; Endocrinopathy; Human; Premature; Intrauterine growth retardation; Pregnancy disorders; Thyroid diseases; Infant; Fetal diseases; Risk factor; Thyroxine; Thyroid hormone
• ISSN: 0378-3782; 1872-6232
• DOI: 10.1016/S0378-3782(01)00172-4

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.
Study design: 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.