Japanese researchers investigating screening tools for gestational diabetes mellitus (GDM) have discovered that the casual blood glucose test (CBG) is less reliable than the 50-g glucose challenge test (GCT).
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The study, published in the Journal of Diabetes Investigation, included 763 pregnant women who underwent both the CBG measurement and the 50-g GCT at 24–28 weeks of gestation. Those who had a blood glucose level ≥140 mg/dL one hour after the GCT were subsequently tested using the 75-g oral glucose tolerance test (OGTT) to diagnose GDM. Overall, 240 women required further testing, with 97 (40.4%) being diagnosed with GDM .
The key finding was that using CBG levels alone, with a threshold of ≥100 mg/dL, would have failed to identify 71.7% of GDM cases that were detected using the GCT. Specifically, 71 out of 99 women who were diagnosed with GDM through the GCT had CBG levels below 100 mg/dL, underscoring the limitations of relying solely on CBG as a screening measure. The study also reported that CBG and GCT results were inconsistent in 38 percent of the cases.
In terms of clinical characteristics, women with GDM or overt diabetes mellitus had higher maternal age, body mass index before pregnancy, and were more likely to have conceived through assisted reproductive technology compared with those without GDM. However, contrary to common expectations, the study noted a lower incidence of multiple pregnancies in the GDM group, though the reasons for this remain unclear.
This study highlights the importance of appropriate screening strategies to prevent missed diagnoses of GDM, which can have long-term health consequences for both mothers and their infants. The authors conclude that, though CBG measurements are less resource-intensive and easier to administer than the GCT, they underestimate the prevalence of GDM. They recommend the use of the 50-g GCT as a more effective screening tool, particularly in regions where CBG is commonly used. Future prospective studies are planned to evaluate the combined use of CBG and the GCT to improve the sensitivity of GDM screening.
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