Background and objectives: Diabetes mellitus is a major public health concern with adverse pregnancy outcome. The objective of this study was to assess the validity of HbA1c as a screening tool in pregnant ladies not known to have diabetes before pregnancy. Patients and methods: Three hundred pregnant women with gestational age between 24 - 28(25.3±2.1) weeks were evaluated for diabetes mellitus using HbA1c, fasting and postprandial plasma glucose for the period of October 2010 - October 2012, using McNamara's test which is expressed as percentages and 95% confidence intervals of the percentages. Results: Of pregnant ladies with non-diabetic fasting plasma glucose values: 79% had HbA1c level of <6.1%, 17% had an HbA1c level of > 6.1% and 5% showed diabetic 2-h plasma glucose values (17% CI 51–71 vs. 5% CI 35–55, respectively; P = 0.007). Of pregnant ladies with diabetic fasting plasma glucose:72% had an HbA1c level of ≥6.1%, 28% had HbA1c level of ≤ 6.0 % and 11% subjects in this group showed nondiabetic 2-h plasma glucose values (28% CI 66 – 86 vs. 11% CI 32–52, respectively; P = 0.003).Of pregnant ladies with postprandial blood glucose >200mg/dL; 42% had normal, 18% had impaired, 39% had high fasting plasma glucose while 71% had HbA1c ≥ 6.1% (71 % CI 51–71 vs. 39% CI 35–55, respectively; P = 0.003). Conclusion: HbA1c is an important alternative screening tool to identify pregnant ladies with undiagnosed diabetes.