ESPE Abstracts

Background: Growth during infancy is a continuation of the rapid fetal growth and its regulation is complex and multifactorial. It is well-established that insulin-like growth factor-I (IGF-I) and its regulators (e.g. IGF binding proteins (IGFBP-3) and pregnancy-associated plasma protein-A2 (PAPP-A2)) are important for prenatal and postnatal growth; however, their significance for growth during infancy is not fully explored.

Aims: The aim of this study was to evaluate length velocity, weight velocity and IGF-I concentrations and to explore the association between length and weight velocities and repeated IGF-I measurements in a large cohort of healthy infants followed prospectively from birth throughout first year of life.

Method: 233 infants (114 girls and 119 boys) participated in the longitudinal COPENHAGEN Minipuberty Study. We examined the infants six times during the first year of life. Length, weight and IGF-I were measured, and length and weight velocities were calculated. The infants were genotyped for PAPPA2 (rs1325598).

Results: Length and weight velocities were high after birth, declined gradually and stabilized around 7^th month of age in both boys and girls, but with markedly higher velocities and steeper declines in boys than in girls. At birth, IGF-I concentrations were higher in girls compared with boys (median concentration 78.7 and 69.5 µg/l, respectively, P = 0.05), and increased significantly from birth to 10 days in boys (mean difference 24.8 ± 34.05 SD µg/l, P < 0.001), but not in girls. Hereafter, IGF-I concentration increased significantly throughout the entire first year of life. In a univariate analysis, both mean length velocity (standard deviation score (SDS)) and mean weight velocity (SDS) were positively associated with mean IGF-I (SDS) (β=0.12 (95% CI, -0.0001-0.24), P = 0.05 and β=0.25 (95% CI, -0.14-0.08), P < 0.001). However, in a multiple regression analysis, only mean weight velocity (SDS) remained associated with IGF-I after adjusting for confounding factors (feeding pattern, birth weight, target height, body fat %, and PAPPA2 genotype) (β=0.19 (95% CI, 0.05-0.33), P = 0.01).

Conclusion: We present individual growth trajectories during the first year of life in 233 Danish infants. Weight velocity, but not length velocity, was positively associated with serum IGF-I concentration, but not PAPPA2 genotype. This indicates that IGF-I promotes an overall gain in weight rather than length during first year of life.