Diagnosis of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is associated with a high risk of obstetric and neonatal complications. Adequate diagnosis and appropriate treatment are key to prevention of these complications. Most international guidelines have adopted the IADPSG 2010/WHO 2013 diagnostic criteria, for the diagnosis of GDM by recommending the following glycemic thresholds for a 75 g OGTT: fasting plasma glucose value =5.1 mmol/l (92 mg/dl); 1-h value =10.0 mmol/l (180 mg/dl); and 2-h value =8.5 mmol/l (153 mg/dl). These specific cut-off values were chosen because they predict a 75% higher chance of adverse pregnancy outcomes compared to normal glucose values. Some countries have adopted either higher levels for fasting glucose (5.6 or 7.0 mmol/l) or lower levels for 2-h post-OGTT glucose (7.8 mmol/l). There still is some debate whether it is desirable to lower the diagnostic 2-h glucose thresholds to =7.5 mmol/l for Caucasian women and =7.2 mmol/l for women from South Asian background. Several studies have shown that about 20-30% (depending on the applied diagnostic criteria) of the women screened for GDM had/have abnormal OGTT results, necessitating referral, active counseling, and treatment. By adopting the new IADPSG/WHO diagnostic criteria, the prevalence of GDM has increased, which has a major impact on the costs and the capacity of healthcare systems. Screening for GDM may follow either a one-step or a two-step approach. In the one-step approach, GDM is diagnosed based on the results of a single 75 g OGTT. The two-step screening strategy makes use of a non-fasting 50 g glucose challenge test (GCT), whereby an abnormal test result (i.e., a 1-h plasma glucose value =7.8 mmol/l) is followed by a 100 g OGTT. There also is no international consensus on whether universal or risk factor-based screening is preferred. Universal screening implies that all pregnant women will undergo screening between 24 and 28 weeks of pregnancy, while in selective screening, only women who have specific risk factors for developing GDM or who exhibit a possible consequence of hyperglycemia, i.e., macrosomia or polyhydramnios, will undergo an OGTT. Most studies comparing these strategies have mainly reported data on GDM classification, not on GDM treatment or, even better, pregnancy outcomes. Some countries, therefore, follow a hybrid approach of partly risk factor-based and partly universal screening. Recently published systematic economic evaluations support universal screening and the one-step approach as a more likely cost-effective strategy.