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

Abstract

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. 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. 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. 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.