Fetal ductus venosus flow assessment can be useful in a number of situations in fetal ultrasound:
first-trimester screening for aneuploidic anomalies
-
second and third-trimester scanning when there are concerns regarding
Of all the precardiac veins, the ductus venosus allows the most accurate interpretation of fetal cardiac function as well as myocardial hemodynamics 9.
Radiographic assessment
Ultrasound
Technique
-
the fetus should be as still as possible
variability in the heights of the S and D waves may indicate fetal breathing, which is normal, but wait for the fetus to be more still before evaluating
the probe is ideally focused so sampling is done where the umbilical vein joins the ductus venosus
a right ventral mid-sagittal view of the fetal trunk should be obtained and color flow mapping used to demonstrate the umbilical vein, ductus venosus and fetal heart
the probe is ideally angled to allow a mid sagittal plane or a transverse oblique plane through the fetal abdomen
the image should be magnified enough for the fetal thorax and abdomen to occupy the whole screen
do not contaminate the ductus venosus flow with the flow from the fetal inferior vena cava, for this the Doppler sample should be small (0.5-1 mm)
the insonation angle should be 30° or less
the sweep speed should be high (2-3 cm/s) so that the waveforms are spread allowing better assessment of the A wave
set the wall filter low enough so that the A wave is not obscured 10
On Doppler ultrasound, the flow in the ductus venosus has a characteristic triphasic waveform where in a normal physiological situation flow should always be in the forward direction 7 (i.e. towards the fetal heart).
This triphasic waveform comprises of:
S wave: corresponds to fetal ventricular systolic contraction and is the highest peak
D wave: corresponds to fetal early ventricular diastole and is the second highest peak
-
A wave: corresponds to fetal atrial contraction and is the lowest point in the wave form albeit still being in the forward direction
as above, reversal of the A wave (i.e. crossing the baseline) is always abnormal 10