title: Multivariate Analysis of Thyrotropin in Preterm Newborns Based on Adequacy of Weight for Gestational Age.
abstract: Different and conflicting data have been published concerning thyrotropin (TSH) levels among small-for-gestational-age (SGA) and appropriate-for-gestational-age (AGA) newborns. The hypothesis of this study was that SGA preterm infants have higher TSH levels than those who are not underweight do.
  
  
  
  This cross-sectional study analyzed the TSH levels of all preterm newborns with a negative congenital hypothyroidism screening result (TSH <7.5 μIU/mL). Secondary variables were sex, birth weight (SGA, AGA), days of life at blood extraction, maternal origin, gestational age, and being a twin or not. Two multiple linear regression models were constructed comparing TSH levels in SGA and AGA or the z-score for birth weight and the remaining variables.
  
  
  
  A sample including 5819 preterm infants was obtained: 53.8% male, 23.3% twins, and 3.3% SGA. TSH concentrations were 2.16 ± 2.0 μIU/mL for the SGA infants and 1.80 ± 1.5 μIU/mL for the AGA infants (p = 0.012), with a negative correlation (p < 0.001) between TSH levels and the z-score for the weight of the newborn. The multivariate analysis comparing TSH levels between SGA and AGA gave the following: SGA (B = 0.46, p < 0.001), Latin American mother (B = -0.16, p = 0.029), days of life at blood extraction (B = -0.26, p < 0.001), and gestational age ≤28 weeks (B = -0.56, p < 0.001). Using the z-score for the weight, the associations were: maternal origin North Africa (B = 0.19, p = 0.042), days of life at blood extraction (B = -0.27, p < 0.001), gestational age ≤28 weeks (B = -0.55, p < 0.001), and z-score for weight (B = -0.12, p < 0.001).
  
  
  
  Our multivariate analysis suggests that TSH concentrations are higher in SGA infants than they are in AGA infants, and this should be taken into account when establishing a reference interval appropriate for this population. The clinical relevance remains unknown, but lines of research are opened that may allow a better understanding of the long-term morbidities in these newborns.
authors.affiliation: 1 Department of Surgery, Pediatrics, Obstetrics, and Gynecology, University of Murcia , Murcia, Murcia, Spain .
authors.forename: Vicente María
authors.initials: VM
authors.lastname: Bosch-Giménez
authors.affiliation: 2 Department of Clinical Medicine, Miguel Hernández University , San Juan de Alicante, Alicante, Spain .
authors.forename: Antonio
authors.initials: A
authors.lastname: Palazón-Bru
authors.affiliation: 3 Department of Pharmacology, Pediatrics, and Organic Chemistry, Miguel Hernández University , San Juan de Alicante, Alicante, Spain .
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Blasco-Barbero
authors.affiliation: 3 Department of Pharmacology, Pediatrics, and Organic Chemistry, Miguel Hernández University , San Juan de Alicante, Alicante, Spain .
authors.forename: Mercedes
authors.initials: M
authors.lastname: Juste-Ruiz
authors.affiliation: 4 Department of Nursing, University of Alicante , San Vicente del Raspeig, Alicante, Spain .
authors.forename: María Mercedes
authors.initials: MM
authors.lastname: Rizo-Baeza
authors.affiliation: 3 Department of Pharmacology, Pediatrics, and Organic Chemistry, Miguel Hernández University , San Juan de Alicante, Alicante, Spain .
authors.forename: Ernesto
authors.initials: E
authors.lastname: Cortés-Castell
mesh_terms: D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood*; D007236:Infant, Small for Gestational Age / Q000097:blood*; D008297:Male; D015999:Multivariate Analysis; D013972:Thyrotropin / Q000097:blood*
chemical_list: D013972:Thyrotropin
keywords: gestational age; intrauterine growth; newborns; preterm; thyrotropin