Introduction: Insulin resistance during pregnancy is associated with adverse effects on foetal and maternal health, including macrosomia, congenital malformations, perinatal mortality and pre-eclampsia. A 100 g Oral Glucose Tolerance Test (OGTT) is recommended by World Health Organisation (WHO) as the diagnostic test for Gestational Diabetes Mellitus (GDM). However, the inconvenience caused to the pregnant females due to time consuming and cumbersome multi-invasive procedure for performing OGTT has prompted the exploration of an alternative method. Aim: To ascertain whether Glycated Haemoglobin (HbA1c) can be used instead of OGTT for diagnosis of GDM. Materials and Methods: It was a case-control study which was conducted for one year from June 2012 to May 2013. In this study, 200 pregnant females with gestational age from 22-40 weeks underwent Fasting Blood Sugar (FBS), Glucose Challenge Test (GCT) with 50 g glucose load, OGTT and HbA1c investigations. Results: The mean HbA1c of Group 1 with GDM was 5.29±0.68% and mean HbA1c of Group 2 without GDM was 4.83±0.46%. At the HbA1c cut-off of ≥5.85%, 18% of GDM patients were identified with specificity of 97%. A higher HbA1c cut-off of ≥5.95% showed sensitivity and specificity of 16.3% and 70%, respectively. An arbitrary cut-off of ≥5.85% would have diagnosed only 18% of patients with GDM with reasonable specificity. According to this study, 88% of GDM cases stayed undiagnosed by HbA1c at a cut-off of ≥5.85%. Hence, it can play only a supplemental role to OGTT in diagnosing GDM. Conclusion: On the basis of the present study, HbA1c can be used as a supplemental investigation in addition to OGTT for confirmation of GDM in pregnant females. Only drawback was the lack of fixed HbA1c cut-off for diagnosing GDM.