Ultrasonographic velocimetry of the fetal ductus venosus.

In fetal lambs, the ductus venosus shunts well-oxygenated blood directly to the heart, a pattern expected to be found also in the human fetus. We aimed to describe the human ductus venosus in a longitudinal sonographic study of two-dimensional imaging, colour flow mapping, and pulsed doppler velocimetry every 3-4 weeks during the second half of pregnancy. The fetuses of 29 healthy women were studied. The ductus venosus and its blood flow were identified and recorded for later analysis that included maximum velocity tracing. In the 184 examinations analysed, the ductus venosus appeared as a narrow vessel projecting a high-velocity jet posteriorly to reach the foramen ovale. The mean peak velocity in the ductus venosus increased from 65 cm/s in week 18 to 75 cm/s at term. Low values of the time-averaged maximum velocity were found in 2 fetuses with cardiovascular abnormalities (1 supraventricular tachycardia, 1 congestive heart failure), as a result of reversed flow in the ductus venosus during atrial systole. The high peak velocity in the ductus venosus, which is comparable with arterial velocities, probably gives the blood sufficient momentum to reach the foramen ovale without extensive mixing with deoxygenated blood. Velocimetry of the ductus venosus carries new diagnostic possibilities.