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Growth-restricted premature infants are at increased risk for low thyroxine
C R Martin1, L J Van Marter, E N Allred
1Department of Neonatology, Beth Israel Deaconess Medical Center, Division of Newborn Medicine, Boston, MA, USA. cmartin1@caregroup.harvard.edu
Insights
Growth restriction in extremely preterm infants is linked to lower early thyroid hormone (thyroxine) levels. This association, possibly influenced by prenatal factors, suggests increased risk for thyroid issues and related complications.
Area of Science:
- Neonatalogy
- Endocrinology
- Perinatal Medicine
Background:
- Extremely premature infants face numerous health challenges.
- Thyroid hormone levels are critical for development and growth.
- Growth restriction is a common complication in preterm neonates.
Purpose of the Study:
- To investigate the association between growth restriction and early serum total thyroxine levels in extremely preterm infants.
- To identify maternal, prenatal, perinatal, and neonatal factors influencing this relationship.
Main Methods:
- A cohort of 719 infants with gestational age 23-30 weeks was studied.
- Serum thyroxine and birth weight were measured within the first week of life and expressed as z-scores.
- Infants of mothers with thyroid disease were excluded; analyses were adjusted for confounders.
Main Results:
- A significant inverse relationship was observed: a 1.0 decrease in birth weight z-score correlated with a 0.18 decrease in total thyroxine z-score (p=0.0001).
- This association remained significant after adjusting for multiple maternal, prenatal, perinatal, and neonatal variables.
- No specific confounding factors were identified to explain the observed relationship.
Conclusions:
- Early total thyroxine levels in extremely preterm infants are significantly associated with birth weight z-score, suggesting antenatal influences.
- Growth-restricted preterm infants exhibit an increased risk of early hypothyroxinemia.
- This finding highlights potential risks for morbidities associated with early hypothyroxinemia in growth-restricted preterm infants.
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.