The use of the new International Association of the Diabetes and Pregnancy Study Groups criteria (IADPSGC) for the diagnosis of gestational diabetes mellitus (GDM) results in an increased prevalence of GDM. Whether their introduction improves pregnancy outcomes has yet to be established. This study sought to evaluate the cost effectiveness of one-step IADPSGC for screening and diagnosis of GDM compared with traditional two-step Carpenter-Coustan (CC) criteria.