Objective: To evaluate the cutoff value of the 1-hr, 50-gram glucose challenge test (GCT) for screening of gestational diabetes mellitus (GDM), in high-risk pregnancy, and to determine the prevalence of GDM in this group.
Study design: Descriptive study (Diagnostic test).
Subjects: Eight hundred and thirty-eight pregnant women, 24-28 weeks, were identified and recruited based on risk indicators between January and October 2004.
Material and Method: A GCT was performed in this group. All women with plasma glucose value ≥130 mg/dl were given a 3-hr, 100-gram glucose tolerance test (OGTT) to diagnose gestational diabetes mellitus using Carpenter and Coustan diagnostic criteria. The receiver-operator characteristic (ROC) curve was used to identify the cut-off value of GCT for detecting GDM. Main outcome measures: The cut-off value of GCT for detecting GDM by using ROC curve with the sensitivity and specificity of various cut-off values.
Results: The ROC curve identified a GCT value of ≥140 mg/dl as the cut-off value for detecting GDM, which showed the sensitivity and specificity of 95.3% and 48.6% respectively. The prevalence of GDM in high-risk pregnant women was 20.17% (169/838).
Conclusions: Recommended threshold of 140 mg/dl used as the cut-off value of 50-gram, 1-hr GCT for screening GDM in high-risk pregnancy.

Keywords: 1 hr; 50 gram glucose challenge test, Screening of gestational diabetes mellitus, High-risk pregnancy