Longitudinal reference ranges for umbilical vein blood flow at a free loop of the umbilical cord

Objective To establish longitudinal reference ranges for the umbilical vein (UV) diameter, velocities and volume blood flow (Q(uv)) at a free loop of the umbilical cord and estimate the UV spatial velocity profile at this site. Methods This was a prospective study of 53 low-risk pregnancies. The UV diameter and blood flow velocities were measured at 4-weekly intervals from 22 + 0 to 39 + 6 weeks of gestation (232 observations) using B-mode ultrasonography and pulsed-wave Doppler. Multilevel regression modeling was used to estimate the reference percentiles. Results The mean UV diameter, velocities and Quv increased with advancing gestation, whereas the Quv normalized for estimated fetal weight decreased. The UV spatial velocity profile coefficient was 0.62. Conclusion We have established reference ranges for serial measurements of Quv at a free loop of the umbilical cord during the second half of pregnancy. The spatial velocity profile of the UV is not completely parabolic at this site. Copyright (C) 2010 ISUOG. Published by John Wiley & Sons, Ltd.