The Diagnostic Value of the 50-Gram Glucose Challenge Test at Various Cut-off Levels Combined with Clinical Risk Factors in Predicting the Diagnosis of Gestational Diabetes Mellitus

Objective: To evaluate the diagnostic precision of the 50-gram glucose challenge test (50-g GCT) at various levels for the detection of gestational diabetes mellitus (GDM), and to examine its association with clinical risk indicators. Material and Methods: At Thammasat University Hospital, our retrospective cohort comprised 1,197 pregnant women screened using the 50-g GCT based on risk factors, including a family history of GDM, obesity, and other factors. Out of these, 219 tested positive, with 83 (37.9%) diagnosed with GDM and 136 (62.1%) without GDM. Comprehensive data including baseline characteristics, as well as maternal and neonatal outcomes, were compiled. We assessed the correlations between clinical risk factors and 50-g GCT values to ascertain GDM. The positive predictive value (PPV) and negative predictive value (NPV) for various cut-off levels were determined. Results: The best cutoff for the 50-g GCT for GDM diagnosis was ≥220 mg/dL with 100% PPV without adding clinical risk. The PPVs reached 75% and 100%, respectively, when combined with maternal age ≥35 years at 50-g GCT thresholds of ≥210 mg/dL and ≥220 mg/dL. A history of diabetes in the family combined with a 50-g GCT provided 100% PPV at 200 mg/dL. Conclusion: A 50-g GCT cut-off value of ≥220mg/dL is proposed for a definitive GDM diagnosis in certain circumstances, negating the need for this additional test. When a pregnant woman has a family history of diabetes, the 50-g GCT cut-off of 200 mg/dL could be a promising marker for identifying GDM.