PURPOSE: We tried to find the relationships between the fetal beta-cell function and neonatal birth weight, anthropometric measures, and maternal characteristics, and to observe role of insulin as fetal growth factor in offsprings of mothers who have normal glucose metabolism. METHODS: We measured umbilical cord blood insulin and C-peptide concentrations in 236 neonates delivered at Cheil General Hospital from Jan. 1 to Jan. 31 1994. Their mothers had normal glucose metabolism during pregnancy. The birth weight and other anthropometric measures were performed within 24 hours after birth by same pediatrician. RESULTS: 1) The mean gestational age was 39.5+/--0.1 wk and mean birth weight was 3.3+/--0.2 Kg. According to birth weight percentile, the numbers of small for gestational age(SGA), adequete for gesational(AGA), and large for gestational age(LGA) infans were 3(1.3%), 178(75.4%), and 55(23.3%), respectively. There were no differences in gestational age, birth weight, length, head circumference, chest circumference, Ponderal index, and symmerty index between male and female infants. 2) The maternal weight gain during pregnancy was related to neonatal birth weight, length, and head circumference, but not to Ponderal index and symmetry index. 3) The mean cord blood insulin and C-peptide concentrations were 5.1+/--0.1uU/ml and 1.3+/--0.1 ng/ml. There was a significant positive correlation between insulin and C-peptide concentrations. 4) There were no significant differences in cord blood insulin and C-peptide concentrations among the SGA, AGA, and LGA group. 5) The cord blood insulin and C-peptide concentrations had weak positive correlations with neonatal birth weight, obesity, and gestational age, but nor with maternal weight gain during pregnancy. CONCLUSIONS: Although insulin has a significant role in fetal growth in diabetic pregnancy or intrauterine growth retardation(IUGR), our results suggest that it does not have a significant effect on fetal growth in offsprings of mothers who have normal glucose metabolism.