Objective The aim of the study was to evaluate the associations between sonographical measurements of the umbilical cord and birth weight in 20-24 weeks of gestations. Methods This cross-sectional study was conducted with the participation of 220 low-risk pregnant women between 20-24 gestational weeks. Biparietal diameter, head and abdominal circumference, and femur length were measured for anthropometric calculations. Umbilical cord including umbilical vein diameters, placental thickness, umbilical artery. Doppler measurements (RI, PI) were recorded. Results In accordance with the results of statistical computations, an inverse relationship was found between umbilical vein diameter and birth weight of a large gestational age (LGA) newborn in 20-24 gestational weeks (p < .05). There was no significant relationship between other parameters and birth weight of LGA newborns. Conclusion There is an inverse relationship between birth weights of newborns with LGA and umbilical vein diamater at 20-24 weeks of pregnancy. The umbilical vein diameter in the second trimester may be a promising measurement on predicting LGA fetus. The researches have not confirmed the physiopathology of this finding yet, but it is paving the path for future studies.