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

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.