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 Q(uv) increased with advancing gestation, whereas the Q(uv) 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 Q(uv) 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 © 2010 ISUOG. Published by John Wiley & Sons, Ltd.