Background: Gestational diabetes mellitus is defined as carbohydrate intolerance with its onset or first recognition during present pregnancy. Objective of present study was to compare screening accuracy of ADA and WHO criteria for screening of gestational DM.Methods: This is a prospective comparative study using ADA and WHO criteria for the screening of GDM. Our objective was to study the implication of implementing the ADA guidelines and WHO guidelines for screening and diagnosis of GDM in 200 antenatal patients at Government Mohankumaramangalam Medical College, Salem during a period of one year from July 2015 to June 2016. All antenatal women attending AN OP between 24-28 weeks of gestation are subjected to fasting blood glucose measurement followed by an oral OGTT using 75 gms of glucose load. Venous blood samples are collected at the end of 1hr and 2hr. The ADA and WHO criteria were applied separately for each subject to diagnose GDMResults: As per ADA criteria presence of any one of either, Fasting blood sugar- 92 mg (5.1 mmol/L),1 hour postprandial-180mg (10.00mmol/L), 2 hour postprandial: 153 mg (8.5 mmol/L) was used for the diagnosis of GDM.As per WHO criteria presence of any one of either, Fasting blood sugar- 126mg/dl (7 mmol/dl) or 2 hour postprandial- 140 mg/dl (7.8 mmol/dl) for diagnosis of GDM. The 2hr value has the statistical significance in the diagnosis of GDM. The 1hr value done in ADA criteria does not have statistical significance when compared to 2hr value.Conclusions: Universal screening for GDM is necessary to diagnose Gestational Diabetes Mellitus. Universal screening may not be feasible in resource poor settings, but it definitely improves the pregnancy outcomes considering the high prevalence of gestational diabetes in India.