Background: Appropriate intrauterine fetal growth and development are fundamental for newborn health and lifelong welfare. Bi-parietal diameter provides the closest correlation with gestational age in second trimester. Objectives: 1. To establish the reference tables for bi-parietal diameter in normal singleton pregnant women from 20 to 38 weeks of gestation from Belagavi District, Karnataka. 2. To find out the predictive accuracy of gestational age determined by bi-parietal diameter measurements with gestational age by menstrual history. Materials and Methods: The data was collected by using predesigned pretested questionnaire from September 2016 to January 2018. Total 768 singleton pregnant women with minimum 30 cases for each gestational week from 20 to 38 weeks of gestation were studied. Statistical Analysis: Data was analysed by Percentages, mean, standard deviation, range, standard error, percentiles and regression equation etc. Results: The regression equation derived for bi-parietal diameter (BPD) measurements was GA = (1.275 + (3.905 X BPD in cm) where __ampersandsignldquo;R2__ampersandsignrdquo;- the proportion of variation in dependent variable (GA) was 0.944 and __ampersandsignldquo;r__ampersandsignrdquo;- the correlation coefficient was 0.9. By using the common regression equations for GA from 20 to 38 weeks, there was a difference of 1.44 to 2.22 weeks in actual and predicted GA at 36 to 38 weeks of pregnancy. However, the same difference was less between 20 to 35 weeks of gestation. Conclusion: The present study findings confirmed that the fetal BPD measurements significantly vary among different population groups. So generation of population specific reference tables by a large scale study is required for more precise reporting by ultrasonography.