Is Non Fasting Glucose Challenge test sensitive enough to diagnose Gestational Diabetes Mellitus?

Background: There is a no consensus over the most sensitive and practical approach to diagnose Gestational Diabetes Mellitus (GDM). The standard 75 grams glucose tolerance test (GTT) is widely practiced to diagnose GDM. However, non-fasting 75-gram Glucose Challenge Test (GCT) with the 2-hour cutoff value of ≥ 140mg/dL is also recommended by some professional bodies. The aim of this study was to investigate the sensitivity and specifiity of GCT when compared to GTT for diagnosing GDM. Methods: Pregnant women in period of gestation between 24- 28 weeks were recruited by simple random sampling method. Non fasting 75g GCTs were performed in all followed by fasting 75g GTTs within a week time. International Association of the Diabetes and Pregnancy Study Groups (IADPSG) criteria of GTT were used as t he reference test to diagnose GDM and 2-hour value of GCT was compared. Findings: According to IADPSG criteria, 21.5% (59/274) of pregnant women had GDM, in compared to 13.1% (36/274) detected by GCT. Sensitivity and specifiity of GCT were 40.6% and 94.4% respectively. The area under the ROC curve for the ability of 2-hour value of GCT to predict GDM detected by GTT was 0.758 (SE 0.039). According to GTT values, FBS ≥ 92 mg/dL alone recognized 11.7% (32/274) of study sample as having GDM. Additional 9.1% (25/274) and 0.7% (2/274) of GDM cases were detected with 1-hour value≥180 mg/dL and 2-hour hour value ≥ 153 respectively. Conclusion: GCT with 2-hour cutoff value ≥ 140mg/dL is not sensitive enough to diagnose GDM recognized by GTT.