INSULIN-LIKE GROWTH-FACTOR (IGF)-I AND IGF-BINDING PROTEIN 3 DURING THE FIRST YEAR IN TERM AND PRETERM INFANTS

Plasma IGF-I and IGF-binding protein 3 (IGFBP-3) were determined by ra dioimmunoassay in term infants (n = 51) at 0, 2, 4, 6, and 12 mo and p reterm infants (n = 51) at -3 (28.4 wk postconceptional age), -2, -1.5 , -1, 0, 2, 4, 6, 9, and 12 mo from expected term. The effects of gest ational age at birth (term or preterm) and study age were determined b y repeated measures analysis of variance and Fisher's least squares di fference. In preterm infants, IGF-I increased between -3 and 2 mo from 0.75 to 10.4 nM, decreased between 2 and 9 mo to 7.3 nM, and increase d again between 9 and 12 mo to 10.1 nM (p < 0.0001), whereas IGFBP-3 i ncreased relatively little from -3 to 0 mo (14.2 to 30.2 nM, p < 0.05) and plateaued from 2 to 12 mo (49.8 to 62.3 nM). At 0 mo, IGF-I and I GFBP-3 were the same in term and preterm infants, but preterm infants had higher IGF-I from 2 through 12 mo (p < 0.05), higher IGFBP-3 at 2 and 4 mo (p < 0.05), and lower IGFBP-3 at 12 mo (p < 0.05). IGF-I and IGFBP-3 were correlated at most ages. First year IGF-I and IGFBP-3 are influenced by study age and by gestational age even after adjusting f or early birth.