Gestation Diabetes mellitus is a condition which leads to unfavorable maternal as well as fetal outcomes. Although the traditional method of screening GDM in pregnant women by OGTT has been widely used and accepted for decades, but there is always a need for better and more easier test for diagnosis of GDM. In our systematic review we have critically appraised few published studies for the demonstration of HbA1c as a diagnostic tool for GDM. It is understood from all these studies HbA1c evaluation have various advantages over the traditional OGTT because of the high reproducibility and improved instrumentation and standardization of HbA1c assay, less biological variability and it is not affected by short term lifestyle changes. It can be used as a primary screening test for all the pregnant women as does not require extensive patient preparation and less time consuming. But once the HbA1c value falls above the reference range it is mandatory to perform a confirmatory test for the diagnosis of GDM. In near future HbA1c can be used as a marker for diagnosis.