Comparison of Glycosylated Hemoglobin (HBA1C) And Oral Glucose Tolerance Test (OGTT) In Gestational Diabetes Mellitus

Abstract

Background: Gestational diabetes mellitus (GDM) is associated with adverse maternal and fetal outcomes, and timely diagnosis is crucial. The oral glucose tolerance test (OGTT) is the current gold standard, but it is time-consuming, inconvenient, and often poorly tolerated. Glycosylated hemoglobin (HbA1c) offers practical advantages as it does not require fasting and reflects long-term glycemic control.

Aim: To compare HbA1c and OGTT in the diagnosis of GDM.

Methods: This case control study was conducted on 190 pregnant women between 24–28 weeks of gestation, divided into two groups: Group I (n=95 healthy controls) and Group II (n=95 diagnosed GDM cases). All participants underwent a standard 75 g OGTT with 2 hours, along with HbA1c estimation. Statistical analysis included Student’s t-test, Pearson correlation, ROC analysis, and calculation of sensitivity, specificity, predictive values, and accuracy.

Results: Women with GDM had significantly higher HbA1c (6.00 ± 0.50%) compared to controls (5.10 ± 0.30%, p<0.001). OGTT values ( 2-hour) were also significantly elevated in the GDM group (all p<0.001). HbA1c correlated strongly with OGTT values, especially with 2-hour plasma glucose (r=0.71, p<0.001). Using a diagnostic cut-off of ≥5.7%, HbA1c yielded sensitivity of 82%, specificity of 90%, PPV of 89.1%, NPV of 83.3%, and accuracy of 86%. Feasibility assessment revealed that HbA1c required less time, lower cost, and was better tolerated compared to OGTT.

Conclusion: HbA1c demonstrates good diagnostic performance and high feasibility in comparison with OGTT. While it cannot fully replace OGTT, it may serve as a valuable adjunct and potential screening tool for GDM, particularly in resource-limited settings.