Antenatal surveillance

In the assessment of impedance to flow:

• It is important to obtain a continuous trace of the waveform from start to the beginning of the next. In arterial vessels automatic tracing software could be used but for venous vessels the triphasic waveform is not appropriately analyzed and therefore the waveform should be traced manually

• In both arterial and venous vessels it is recommended that the pulsatility index (PI) is measured and reference ranges are used to interpret the results

In the assessment of a hyperdynamic circulation, as in fetal anemia, the peak systolic velocity (PSV) which is highest point of the Doppler envelope should be considered

Doppler ultrasound calculator

You can enter the values from your patient and see them plotted on the normal ranges of  uterine artery PI, umbilical artery PI, ductus venosus PI and middle cerebral artery PI and peak systolic velocity