Objectives To explore the relationships between postmenstrual age (PMA), insulin, C-peptide, glucagon and blood glucose concentrations (BGCs) in preterm and term neonates. To compare glucagon-like peptide-1 (GLP-1) concentrations in fed versus never-fed neonates.

Design Observational.

Setting Dunedin Hospital Neonatal Intensive Care Unit, New Zealand.

Patients Term or preterm euglycaemic neonates (102) receiving routine blood tests (343 samples).

Interventions None: plasma was obtained from surplus samples from routine clinical care.

Main outcome measures Insulin, C-peptide, GLP-1 and glucagon concentrations were measured in temporal association with BGC.

Results Insulin and C-peptide concentrations were elevated in very preterm infants (PMA≤32 weeks) and decreased to term; this relationship persisted when BGCs were accounted for. Generalised linear mixed models showed that insulin:C-peptide ratio and insulin:BGC ratio decreased significantly with increasing PMA (p<0.001). GLP-1 increased following initial oral feeds regardless of PMA (p<0.001).

Conclusion Preterm neonates exhibit insulin resistance in the absence of hyperglycaemia. Enteral feeds result in an increase in GLP-1. These factors are likely to contribute to the increased risk of hyperglycaemia in premature neonates (PMA<32 weeks).