Hyperglycaemia following glucose challenge test during pregnancy: When can a screening test become diagnostic?

Abstract

Objective The 50 g-glucose challenge test (GCT) is commonly used for screening of gestational diabetes (GDM) in low risk pregnant women. If elevated, glucose tolerance test is performed to confirm the diagnosis. In this study, we evaluated whether GCT alone is sufficient to diagnose GDM when the GCT result is very elevated. Research design and methods Using a database of 62877 pregnancies over 10 years, the positive predictive value (PPV) of GCT for GDM was assessed using different GCT cut-off values. Results At a glucose cut-off value of 11 mmol/l, the PPV for GDM was 85.3%, based on the subsequent GTT. This increased to 95.3% when the cut-off was 12 mmol/l. Furthermore, the PPV was consistently higher when GCT was performed in the morning. Conclusion We concluded that the diagnosis of GDM can be made when the glucose level following GCT is very elevated, and GTT need not to be performed for confirmation of GDM. The timing of GCT also affected PPV for GDM, and has implications on the diagnostic value of the test.