Gestational diabetes mellitus (GDM), defined as hyperglycaemia first recognised during pregnancy, is an important clinical entity, especially with its impact on pregnancy outcomes and the increased risk of metabolic disease for both mother and child in their later lives. However, the definition and diagnosis of GDM have continued to evolve over the past 50 years, and this has sometimes caused confusion for clinicians. Currently, different countries adopt different strategies in diagnosing GDM, despite a previous attempt in 2008 to decide on a universally acceptable diagnostic algorithm. In this review, the biological principles that underpin dysglycaemia in pregnancy, the evolution of diagnostic standards for GDM over the years, reasons for the different diagnostic criteria and recognition of early versus late GDM will be discussed. The controversies and uncertainties, pitfalls and alternate ways to diagnose GDM will also be explored.

gestational diabetes mellitus

pregnancy

screening

first trimester

macrosomia

breastfeeding

neonatal intensive care

© 2025 The Authors. Published by Elsevier Ltd.