Diagnosing gestational diabetes mellitus: implications of recent changes in diagnostic criteria and role of glycated haemoglobin (HbA1c).

Gestational diabetes mellitus (GDM; approximately 5% of pregnancies) represents the most important risk factor for development of later-onset diabetes mellitus. We examined concordance between GDM diagnosis defined using the original 1999 World Health Organization (WHO) criteria and the more recent 2013 WHO criteria and 2015 National Institute for Health and Care Excellence (NICE) criteria. We studied two groups: a case-control group of 257 GDM positive and 266 GDM negative cases, and an incident cohort 699 GDM positive and 6,231 GDM negative cases. In the incident cohort, GDM prevalence was 3.7% (WHO 1999 criteria), 11.4% (NICE 2015 criteria) and 13.7% (WHO 2013 criteria). Our results showed that a significant number of additional cases are detected using the more recent NICE and WHO criteria than the original 1999 WHO criteria, but these additional cases represent an intermediate group with 'moderate' dysglycaemia (abnormal blood glucose levels). Our results also show that use of these newer criteria misses a similar group of intermediate cases that were defined as GDM by the 1999 WHO criteria and that glycated haemoglobin in isolation is unlikely to replace the oral glucose tolerance test in GDM diagnosis.