BACKGROUND Recommendations to change the diagnostic criteria for gestational diabetes mellitus (GDM) are controversial. Two sets of criteria are currently in use in Australia, which has led to considerable confusion. OBJECTIVE This article discusses the rationale behind the proposed changes to the diagnostic criteria, and aims to clarify the current approach to the testing for and diagnosis of GDM in Australia. DISCUSSION Gestational diabetes mellitus has adverse effects on pregnancy outcomes and implications for the long term wellbeing of mother and infant. New information about the relationship between hyperglycaemia in pregnancy and fetal outcomes has led to the formulation of revised recommendations for testing and diagnosis of GDM. The changes to the diagnostic threshold will increase the numbers of women diagnosed with GDM by up to 50%. Evidence that management of GDM improves neonatal outcomes mandates a proactive approach to diagnosis and management. General practitioners will have an increasing role in managing GDM.