PURPOSE: To determine whether serum insulin and glucagon levels of umbilical cord blood correlate with subsequent postnatal hypoglycemia in appropriate for gestational age (AGA) - preterm infants at different gestational ages (GAs). METHODS: The serum insulin and glucagon levels of umbilical cord blood were measured using magnetic bead based multiplex immunoassay in 69 AGA - premature infants, stratified according to GA: GA 23-30 weeks, early preterm (EP, n=31); GA 31-34 weeks, late preterm (LP, n=38). Postnatal hypoglycemia was defined as a capillary glucose level <40 mg/dL within the first 60 minutes of life, regardless of GA. RESULTS: The capillary glucose concentration in EP infants (65.5±21.2 mg/dL) was significantly higher than that of LP infants (55.9±17.3 mg/dL) (P=0.043). The serum glucagon level in EP infants (44.3±28.7 pg/mL) was significantly higher than that in LP infants (28.1±13.6 pg/mL) (P=0.006). There was not a significant difference in serum insulin level between EP and LP infants (372.7±254.2 pg/mL vs. 372.4±209.1 pg/mL, P=0.996). There was a significant difference in the serum glucagon level between infants with and without hypoglycemia (27.7±8.9 mg/dL vs. 36.8±24.6 mg/dL, P=0.036), but not in the serum insulin level (451.9±256.9 pg/mL vs. 357.4±222.2 pg/mL, P=0.211). Postnatal glucose concentration within the first 60 minutes of life had a significant positive correlation with serum glucagon levels (r=0.256, P=0.034), but not with serum insulin levels (r=-0.020, P=0.867). CONCLUSION: Lower glucagon levels of cord blood were seen in premature infants with higher GA, which might contribute to the occurrence of postnatal hypoglycemia.