title: A prospective study of serum insulin-like growth factor I (IGF-I) and IGF-binding protein-3 in 942 healthy infants: associations with birth weight, gender, growth velocity, and breastfeeding.
abstract: BACKGROUND
  Many aspects of hormonal regulation and mechanisms of normal infancy growth are poorly understood.
  
  
  OBJECTIVE
  The objective of this study was to establish the determinants of serum growth factor levels in infancy and their association with growth.
  
  
  METHODS
  A prospective, longitudinal, population-based birth cohort between 1997-2001 was studied.
  
  
  METHODS
  Study participants were 942 healthy appropriate weight for gestational age (AGA) infants (538 boys and 404 girls) and 49 small for gestational age (SGA) children (29 boys and 20 girls).
  
  
  METHODS
  INTERVENTIONS were anthropometrical measurements (0, 3, 18, and 36 months) and serum samples (3 months).
  
  
  METHODS
  Height, weight, and serum IGF-I and IGF-binding protein-3 (IGFBP-3) were the main outcome measures.
  
  
  RESULTS
  IGF-I levels showed no gender difference [boys, 92 ng/ml (confidence interval, 49, 162); girls, 91 ng/ml (47, 149); P = 0.50]. IGFBP-3 levels were significantly higher in females [2174 ng/ml (1295, 3330)] than in males [2103 ng/ml (1266, 3143); P = 0.04]. Infants receiving breast milk had lower IGF-I levels [90 ng/ml (48, 154)] than infants receiving formula [n = 62; 97 ng/ml (58, 165)] or both [n = 123; 94 ng/ml (48, 169); P < 0.001]. IGF-I and IGFBP-3 levels were positively associated with weight gain and height gain from birth to 3 months of age in AGA, but not in SGA, children. SGA children had significantly lower IGF-I [88.0 ng/ml (28, 145); P = 0.05] and IGFBP-3 [1835 ng/ml (1180, 2793); P < 0.001] levels than AGA children.
  
  
  CONCLUSIONS
  We found a significant, but weak, association between IGF-I and IGFBP-3 levels at 3 months and postnatal growth in AGA, but not SGA, children. Factors other than IGF-I must contribute to the regulation of normal postnatal growth, and these may differ between AGA and SGA children. IGFBP-3, but not IGF-I, showed a gender difference, which may reflect an influence of the postnatal activation of the pituitary-gonadal axis on binding protein levels.
authors.affiliation: University Department of Growth and Reproduction, Section-GR 5064, Rigshospitalet, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Chellakooty
authors.forename: A
authors.initials: A
authors.lastname: Juul
authors.forename: K A
authors.initials: KA
authors.lastname: Boisen
authors.forename: I N
authors.initials: IN
authors.lastname: Damgaard
authors.forename: C M
authors.initials: CM
authors.lastname: Kai
authors.forename: I M
authors.initials: IM
authors.lastname: Schmidt
authors.forename: J H
authors.initials: JH
authors.lastname: Petersen
authors.forename: N E
authors.initials: NE
authors.lastname: Skakkebaek
authors.forename: K M
authors.initials: KM
authors.lastname: Main
mesh_terms: D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D001724:Birth Weight; D001942:Breast Feeding; D015331:Cohort Studies; D005260:Female; D006128:Growth / Q000502:physiology*; D006801:Humans; D007223:Infant; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D012016:Reference Values; D012727:Sex Characteristics
chemical_list: D015415:Biomarkers; D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I