C-PEPTIDE, INSULIN-LIKE GROWTH FACTOR-I AND FACTOR-II, AND INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-1 IN UMBILICAL-CORD SERUM - CORRELATIONS WITH BIRTH-WEIGHT

OBJECTIVE: Our purpose was to determine the correlation between birth weight and hormones or growth factors believed to be involved in fetal growth: insulin, insulin-like growth factors I and II, and insulin-li ke growth factor binding protein-1. STUDY DESIGN: Five hundred thirty- eight cord serum samples were analyzed for insulin-like growth factor- I, insulin-like growth factor-II, C-peptide, and insulin-like growth f actor binding protein-1 by immunoassay. Samples included all gestation al ages in the third trimester and a large range of birth weights. RES ULTS: Cord serum insulin-like growth factor-I concentrations increased until 39 weeks (+84% from 28 to 29 weeks), followed by a 21% decline at 41 weeks. Insulin-like growth factor-I levels were decreased by 40% in small-for-gestational-age (< 10th percentile) newborns and were in creased by 28% in large-for-gestational-age (> 90th percentile) newbor ns in the absence of diabetes. Insulin-like growth factor-I levels wer e best correlated with birth weight (R = 0.48, p < 0.001). Cord serum insulin-like growth factor-II concentrations were sixfold to tenfold h igher than those of insulin-like growth factor-I and were 8% to 10% (p < 0.001) higher in large-for-gestational-age than in average-weight a nd small-for-gestational-age newborns. Cord serum C-peptide concentrat ions were 28% and 34% higher in large-for-gestational-age than in aver age-for-gestational-age and small-for-gestational-age newborns, respec tively. Insulin-like growth factor binding protein-1 levels were incre ased in preterm average-for-gestational-age and in term small-for-gest ational-age newborns compared with term average-for-gestational-age ne wborns and showed a negative correlation with birth weight (R = -0.43, n = 131, p < 0.001). Insulin-like growth factor binding protein-1 was not correlated with C-peptide concentrations. CONCLUSIONS: Insulin-li ke growth factors I and II and insulin are all related to fetal growth and weight gain, and insulin-like growth factor-I correlates best wit h birth weight. Insulin is mainly related to fetal overgrowth (macroso mia). Insulin-like growth factor binding protein-1 may be a growth inh ibitor in the fetus.