INTRODUCTION – The prevalence rate of Gestational Diabetes Mellitus (GDM) is said to reflect the prevalence of Impaired Glucose Tolerance (IGT) in young reproductive women as well as the background prevalence of Type–2 DM in the given population. AIM’S AND OBJECTIVE – To detect gestational diabetes mellitus by DIPSI – single step test. MATERIAL AND METHODS – This study was conducted in 200 patients coming to Pannadhay Rajkiya Mahila Chikitsalaya, RNT Medical College, Udaipur followed throughout their antenatal period in all three trimesters. The incidence and onset gestational diabetes mellitus in antenatal women using Single Step Diagnostic Test (DIPSI criteria by measuring venous plasma levels 2 hours after ingestion of 75 gm oral glucose). RESULTS – In our study population 13.5% women were found to have Gestational Diabetes Mellitus (GDM) and 8% more having Gestational Glucose Intolerance (GGI). Out of that, 37.04% of GDM and 25% GGI were picked up in first trimester only. An incidence of GDM as 15 to 17%, out of that 17% cases were picked up before 16 weeks of gestation. CONCLUSION – Finally we can say, a short term intensive care gives a long term pay off in the primary prevention of obesity, impaired glucose tolerance and diabetes in the offspring, as preventive medicine starts in utero.