Defining Threshold Value of 50-g Glucose Challenge Test to Diagnose Gestational Diabetes Mellitus in At-risk Women

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Patthamaphorn Chongcharoen
Supitcha Sassanarakkit


Background: Gestational diabetes mellitus (GDM) is usually screened by the 50-g glucose challenge test (GCT) and subsequently confirmed its
diagnosis with the 100-g oral glucose tolerance test (100-g OGTT). The very-high glucose level obtained from the 50-g GCT test may be valid
to diagnose GDM and discard the unnecessary 100-g OGTT test.

Objective: To define the threshold value of 50-g GCT using for diagnosis of GDM in the diabetic at-risk pregnant women.

Materials and methods: A diagnostic research was conducted among 552 pregnant women who had ≥1 risk of GDM and received 50-g GCT
in Lampang Hospital between January 2019 and September 2021. In case of blood sugar ≥140 mg/dl, the 100-g OGTT was implemented and
interpreted according to Carpenter & Coustan criteria to diagnose GDM. The results 50-g GCT were categorized with 10 mg/dL increment and
analyzed to define the cut-off value for GDM diagnosis.

Results: The mean age was 31.0 years (SD 5.7) and 407 women (73.7%) were multigravida. Most of 50-g GCT performed at gestational age ≥24
weeks (64.3%). GDM were diagnosed in 178 cases (32.2%) with the 100-g OGTT using Carpenter & Coustan criteria. At the cut-off value of 50-g GCT
≥210 mg/dl, GDM could be diagnosed in 100% of cases. Both specificity and positive predictive value were 100%.

Conclusion: In pregnant woman who has at least 1 risk factor and blood level of 50-g GCT ≥210 mg/dl, diagnosis of GDM could be made without
confirmation by the 100-g OGTT.


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Chongcharoen, P., & Sassanarakkit, S. (2022). Defining Threshold Value of 50-g Glucose Challenge Test to Diagnose Gestational Diabetes Mellitus in At-risk Women. Lampang Medical Journal, 43(1), 7–15. Retrieved from
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