Background: Birth size is associated with long-term morbidity. Insulin-like growth factor (IGF) system is the most important endocrine factor influencing fetal growth. During rapid somatic growth, free-to-total IGF-I ratio is increased, resulting in higher IGF-I bioavailability. The purpose of this study was to investigate the association of free-to-total IGF-I ratios, IGF-II, and IGF-binding protein (IGFBP)-3 umbilical cord levels with anthropometric data of term neonates.
Methods: Umbilical venous plasma samples were obtained from 95 term neonates and analyzed by enzyme-linked immunosorbent assay.
Results: The large-for-gestational age (LGA) neonates had higher free IGF-I, total IGF-I, and IGFBP-3 levels than small-for-gestational age (SGA) neonates (P < 0.01, 0.001, 0.01, respectively) and higher total IGF-I and IGFBP-3 levels than appropriate-for-gestational age (AGA) neonates (P < 0.05, 0.01, respectively). The free-to-total IGF-I ratios and IGF-II levels were not different among SGA, AGA, and LGA neonates. Free IGF-I, total IGF-I, and IGFBP-3 levels were positively correlated with birth weight (r = 0.34, P < 0.001; r = 0.41, P < 0.001; r = 0.25, P < 0.05, respectively). Multiple linear regression analyses revealed that only total IGF-I levels was the independent predictive variable for birth weight.
Conclusions: Our data suggest total IGF-I is the most important factor in the IGF system for determining fetal growth, at least near term gestation. Free-to-total IGF-I ratios may mostly be determined by total IGF-I. If birth size is associated with adult chronic metabolic diseases, total IGF-I may be involved in the pathogenesis.