Association of Umbilical Cord Plasma Acid-labile Subunit of the Insulin-like Growth Factor Ternary Complex with Anthropometry in Term Newborns

Abstract

Birth size can affect neonatal morbidity and mortality. The insulin-like growth factor (IGF) system is the most important endocrine factor influencing fetal growth. In the circulation, IGFs (mostly IGF-I) are bound to IGF-binding protein 3 (IGFBP-3) and an acid-labile subunit (ALS) to form a ternary complex. The ALS protects IGFs from decay and facilitates their endocrine activity. However, the function of ALS in fetal growth has not yet been fully determined. Venous umbilical plasma samples were obtained from 98 term neonates and analyzed using enzyme-linked immunosorbent assays. The ALS, IGF-I, and IGFBP-3 umbilical cord plasma levels were analyzed for their association with anthropometric measurements of the neonates. The ALS, IGF-I, and IGFBP-3 cord plasma levels were positively correlated with birth weight (r=0.42, p<0.001; r=0.43, p<0.001; and r=0.27, p<0.01, respectively) and placental weight (r=0.37, p<0.001; r=0.31, p<0.01; and r=0.30, p<0.01, respectively). In addition, the ALS cord plasma levels were also positively correlated with head circumference (r=0.29, p<0.01). Multiple linear regression analyses showed that both ALS and IGF-I cord plasma levels were independent predictive variables for birth weight (p<0.01 and p<0.005, respectively). The ALS cord plasma levels were the only independent predictive variables, however, for head circumference and placental weight (p<0.01 and p<0.05, respectively). The ALS umbilical cord plasma levels are one important factor, in addition to IGF-I, in the IGF system for predicting birth anthropometry, at least for near-term gestation. Our results suggest that the influence of ALS on the IGF system may develop prior to birth and affect fetal growth.