Aims/hypothesisTo determine the impact of implementing the new WHO-2013 criteria on prevalence of gestational diabetes mellitus (GDM) and pregnancy outcomes compared to the WHO-1999 criteria. MethodsA retrospective study conducted in pregnant women who were referred to the Erasmus MC for an oral glucose tolerance test (OGTT) between 2010 and 2015. ResultsOf 3089 women, 11.5 % (n = 354) were diagnosed with GDM based on the WHO-1999 criteria and 17.0 % (n = 524) based on the 2013–criteria, with 97 (3.1 %) reclassified as non-GDM and 267 (8.6 %) reclassified as GDM when shifting from the 1999 to 2013-criteria. In contrast to 60 % of patients in the WHO-2013 group, only 2 % of the WHO-1999 group was diagnosed with GDM because of an elevated fasting glucose only. Patients reclassified as GDM by WHO-2013 criteria had a higher body mass index (p < 0.001) and delivered babies with a higher birth weight (p = 0.01). Maternal and neonatal adverse outcomes were comparable between patients with GDM based on WHO-1999 criteria and patients newly included by WHO-2013 criteria. ConclusionsImplementing the new diagnostic criteria leads to a considerable increase of prevalence of GDM. The newly included patients were more frequently overweighed and delivered babies with a higher birth weight. The added diagnostic value of the fasting glucose threshold of the WHO-1999 criteria is very low compared to the 2-h post-OGTT threshold, supporting the use of a lower fasting glucose threshold value as advocated by the WHO-2013 criteria. TweetThe new WHO-2013 criteria leads to a considerable increase of prevalence of GDM.