Background: It has been established that presence of lean umbilical cord with reduced Wharton's jelly in sonographic scans is a fetal marker for risk of small for gestational age at birth. With improvement of ultrasound techniques, more studies have been investigating the alterations of the umbilical cord on pregnancy outcomes.

Objectives: To determine the reference ranges of the umbilical cord area during pregnancy and to find out the association between umbilical cord morphometry and fetal anthropometric measurements.

Patients and methods: A cross sectional study was carried out on a study population of 278 low-risk pregnant women between 15 and 41 weeks of gestational age. Fetal anthropometric measurements including biparietal diameter, abdominal circumference, and femur length were calculated. The measurements of the cross-sectional area (CSA) and circumference of the umbilical cord, vein and arteries were done on an adjacent plane to the insertion of umbilical cord into the fetus's abdomen. The mean and standard deviation of the CSA of the umbilical cord and the 5th, 10th, 50th, 90th, 95th percentiles of it were calculated for each gestational age. Pearson correlation coefficient was used to assess the correlation between the measures of the cord and fetal anthropometric measurements. Polynomial regression analysis was performed for curves.

Results: The values of the CSA of the umbilical cord, umbilical vein and Wharton's jelly (WJ) increase consistently until 30 weeks of gestation, after which they reach a plateau. There was a significant correlation between anthropometric measurements and umbilical cord measurements especially with the CSA of the umbilical cord, umbilical vein and WJ. The regression equation for the umbilical cord CSA according to gestational age up to 30 weeks was y = -0.2159 x(2) + 23.828x-325.59 (R(2) = 0.6334) and for the WJ area according to gestational age up to 30 weeks, it was y = -0.2124 x (2) +17.613x-221.66 (R(2) = 0.4979).

Conclusion: Reference ranges for umbilical cord CSA have been generated. The CSA of the umbilical cord and other components of it increase as a function of gestational age. These measurements correlate with fetal size.