The Usefulness of the Glycosylated Hemoglobin Level for the Diagnosis of Gestational Diabetes Mellitus in the Korean Population

BACKGROUND: An oral glucose tolerance test (OGTT) is the current method used for screening and diagnosis of gestational diabetes mellitus (GDM). OGTT is a relatively complicated procedure and is expensive. Thus, new strategies that do not require fasting or more than a single blood draw may improve the diagnosis of GDM and increase the rate of GDM testing. We investigated the utility of monitoring glycosylated hemoglobin (HbA1c) levels for the diagnosis of GDM. METHODS: The data from 992 pregnant women with estimated gestational ages ranging from 24 to 28 weeks were retrospectively reviewed. There were 367 women with plasma glucose levels ≥140 mg/dL 1 hour after a 50-g OGTT. GDM was diagnosed according to the Carpenter-Coustan criteria for a 3-hour 100 g OGTT. A HbA1c assessment was performed at the same time. RESULTS: We enrolled 343 women in this study, and there were 109 women with GDM. The area under the curve the receiver operating characteristic curve for HbA1c detection of GDM was 0.852 (95% confidence interval, 0.808 to 0.897). A HbA1c cutoff value ≥5.35% had maximal points on the Youden index (0.581). The sensitivity was 87.2% and the specificity was 70.9% for diagnosing GDM. A threshold value ≥5.35% indicated that 163 patients had GDM and that 68 (41.7%) were false positive. The positive predictive value was 58.3% at this threshold value. CONCLUSION: Despite substantial progress in methodology, HbA1c values cannot replace OGTT for the diagnosis of GDM.