IGF-I, IGF-II, free IGF-I and IGFBP-1, -2 and -3 levels in venous cord blood: Relationship to birthweight, length and gestational age in healthy newborns

The insulin-like growth factors (IGF-I and IGF-II) and their binding proteins (IGFBPs) have been implicated in regulating fetal growth and development. The aim of this study was to determine whether fetal IGFs correlate with auxologic data at birth and/or gestational age. Venous cord blood was obtained from 138 healthy newborns immediately after birth and clinical data were recorded using a standardized data sheet. For the determination of IGF-I and IGF-II, IGFBP-blocked radioimmunoassays were used. A coated-tube immunoradiometric assay was applied for the measurement of free IGF-I. IGFBP-1, -2, and -3 were measured using specific radioimmunoassays. IGF-I levels were 61 ± 21 ng ml^-1 median 61 ng ml^-1, range 19-114 ng ml^-1; IGF-II levels were 466 ± 80 ng ml^-1, median 457 ng ml^-1, range 311-701 ng ml^-1; free IGF-I levels were 2.4 ± 1.8 ng ml^-1, median 1.8 ng ml^-1, range 0.4-7.8 ng ml^-1. The concentration of IGFBP-1 was 144 ± 110 ng ml^-1, median 113 ng ml^-1, range 20-626 ng ml^-1; that of IGFBP-2 was 1165 ± 455 ng ml^-1, median 1119 ng ml^-1, range 440-3466 ng ml^-1. IGFBP-3 levels were 1272 ± 280 ng ml^-1, median 1272 ng ml^-1, range 600- 1966 ng ml^-1. IGF-I levels correlated significantly with IGFBP-3 levels (r = 0.71), birthweight (r = 0.48) and birth length (r = 0.37). There were significant inverse correlations between IGF-I and both IGFBP-1 (r = -0.45) and IGFBP-2 (r = -0.62). Although free IGF-I levels correlated (r = 0.71) with total IGF-I, only marginally significant correlations were found between free IGF-I and birthweight (r = 0.25). According to multiple regression analysis free IGF-I levels were only dependent upon total IGF-I, IGFBP-2 and IGFBP-1, whereas IGFBP-3 levels did not contribute to the variance of free IGF-I concentrations in venous cord blood. There was no significant correlation between IGF-II and auxologic data at birth. When IGF-I and IGFBP- 3 levels were analysed with respect to gestational age a biphasic pattern with maxima at 270 d was observed. IGFBP-2 exhibited a reversed pattern with a minimum at 265 d of gestation. In conclusion, these data suggest that IGF- I and the IGFBPs, but not IGF-II, play a role in the regulation of late fetal growth and development.