BACKGROUND Gestational Diabetes Mellitus (GDM) is a common metabolic complication in pregnancy with a broad range of adverse foetal and maternal outcomes if not properly managed. Due to the difficult nature of the OGTT, the use of HbA1c test as a simpler, more cost effective and acceptable alternative has been suggested. There is paucity of data in our setting on the effectiveness of HbA1c for GDM diagnosis. OBJECTIVES The main objective of this study was to compare HbA1c and OGTT in the diagnosis of GDM and ascertain the usefulness of HbA1c as a diagnostic test for GDM among antenatal clinic attendees in the UPTH. METHODOLOGY This was a hospital based prospective longitudinal study involving 24-28 weeks pregnant women in the UPTH. Socio-demographic data and results of the OGTT and HbA1c tests were entered in a proforma. Data collected was analysed using SPSS 20.0 for windows® statistical software. Youden index was used to determine the optimal cut–off point for glycated haemoglobin.