Assessment of gestational age is paramount in obstetric care. This study was to evaluate the gestational age (GA) by measuring the Umbilical Cord Diameter (UCD) in the second and third trimester of pregnancy, and to compare the findings with the Femur Length (FL), Bi-parietal Diameter (BPD) and Last Menstrual Period (LMP). Fifty Sudanese Pregnant women underwent routine sonographic examination using 3.5MHz curve liner transducer; the sonographic cross-sectional area of the umbilical cord was measured in a plane adjacent to the insertion of the cord into the fetal abdomen. Maternal age and number of parity have been evaluated. The relation was statistically significant between UCD depth, width and GA. Gestational age can be predicted and can be depicted by the following equations: GA= (1.380 × UCD length +8.160) and GA= (1.545× UCD width+5.943). There was unsubstantial relation between UCD and maternal age. A linear relationship was found between parity and the UCD depth and width. Using paired T-test indicates that the GAs calculated from FL was accurate, there was no significant difference detected between the LMP age and the estimated one and UCD depth, width, but BPD showed significant difference at p = 0.005 .Measuring UCD is useful for the assessment of gestational age. It has a role in obstetric care in the second and third trimester of pregnancy, and these equations can be used to estimate the gestational age instead of BPD and FL.