The Relationship among Intrauterine Growth, Insulinlike Growth Factor I (IGF-I), IGF-Binding Protein-3, and Bone Mineral Status in Newborn Infants
Insulinlike growth factors (IGFs) exert profound effects on somatic growth and cellular proliferation of many tissues and play an essential role in bone metabolism. The aim of this study was to investigate how fetal growth and bone mineralization correlate with IGF-I and IGF-binding protein-3 (IGFBP-3) levels of newborn infants and their mothers. In addition, we aimed to determine the predictive value of anthropometric measurements on variability in bone mineral status. Umbilical cord venous blood samples were obtained at delivery from 100 term newborn infants. Forty of the newborn infants had birthweights appropriate for gestational age (AGA), 30 were small for gestational age (SGA), and 30 were large for gestational age (LGA). Data were acquired using whole-body dual-energy X-ray absorptiometry scanner with a pediatric platform. Umbilical cord serum IGF-I concentrations were higher in LGA newborns ( P < 0.01), but lower in SGA newborns ( P < 0.01) than in AGA newborns. Umbilical cord serum IGFBP-3 concentrations in LGA newborns were significantly greater than in SGA and AGA newborns ( P < 0.01 and P < 0.01, respectively). Whole-body bone mineral density (WB BMD) was higher in LGA babies (0.442 +/- 0.025 g/cm2 [SD]; P < 0.01) but lower in SGA (0.381 +/- 0.027 g/cm 2; P < 0.0001) than in AGA babies (0.426 +/- 0.022 g/cm2). WB BMD and content (WB BMC) were correlated significantly with birthweight, birth height, head circumference, body mass index (BMI) of the infants; ponderal index and triceps skinfold thickness (reflecting fat stores) of the infants; cord serum IGF-I concentration, serum IGF-I concentration of the mothers; and fat mass, proportionate fat mass, weight, and BMI of the mothers. In contrast, WB BMC was also correlated positively with cord serum IGFBP-3 concentration and gestational age, and WB BMD was positively correlated with serum IGFBP-3 levels of the mothers. Umbilical cord serum IGF-I concentration of the infants was correlated significantly with the concentration of the mothers ( R = 0.232; P = 0.020). Umbilical cord serum IGF-I and IGFBP-3 concentrations were correlated significantly with the fat mass, gestational age, birthweight, birth height, head circumference, and BMI of the infants. Umbilical cord IGF-I concentration was also correlated with ponderal index and triceps skinfold thickness of the infants, maternal weight, BMI, and proportionate fat mass of the infants. Stepwise multiple regression analyses showed no significant relation between bone indices (WB BMD, WB BMC) and the infant's or mother's variations including serum IGF-I and IGFBP-3 concentrations. Birthweight and gestational age are related to bone indices. However, the present study does not provide support for the hypothesis that serum IGF-I and IGFBP-3 levels of infants and their mothers may play a major role in the regulation of bone metabolism in the developing skeleton.
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