Assessment of therapy in gestational diabetes by substrate and hormone responses to a standardized test meal

Postprandial substrate and hormone responses to a standard mixed meal (400 kcal) was determined at two occasions, A and B, in 11 women with gestational diabetes (GDMs) and 11 normoglycaemic controls, matched for age, body mass index, and gestational age. Levels of circulating glucose, non-esterified fatty acids (NEFA), glycerol, 3-hydroxybutyrate (3-HBA), individual amino acids, insulin, and C-peptide were analysed. A was performed when GDMs were considered inadequately controlled with diet alone, B later during gestation following initiation of insulin therapy because of hyperglycaemia. Fasting glucose, glycerol, total and individual amino acids (alanine, valine, isoleucine, leucine), insulin, and C-peptide were not different from normal during A and B, neither were postprandial amino acid levels. During test A, GDMs had elevated fasting and postprandial 3-HBA (p < 0.001), greater postprandial rise of glucose (p < 0.001), elevated NEFA (p < 0.05), but normal and parallel decreases of NEFA and glycerol. Insulin and C-peptide responses were delayed and prolonged. During B, GDMs had higher glucose response (p < 0.005), higher fasting 3-HBA (p < 0.02) but similar and parallel decreases of NEFA, glycerol, and 3-HBA as controls. The C-peptide response was not significantly different from normal; insulin response was higher (p < 0.05). In conclusion, the relative insulin deficiency characterizing GDMs, also when treated with insulin, is associated with selected defects in insulin action; mainly affecting glucoregulation, whereas suppression of lipolysis and proteolysis remain normal.