Normal umbilical artery Doppler waveform

Normal umbilical artery waveform. The Doppler affects the magnitude of the Doppler shift, which will be highest when the Doppler beam path (as indicated by the cursor line) is parallel to the vessel axis and the angle is thus close to 0 degrees (Panel A). In this setting, the Doppler shifts will measure the true velocity of blood flow. By contrast, the magnitude of the shift will be lowest when the beam path is perpendicular to the vessel axis (angle is 90 degrees) and the velocity will be underestimated (Panel B). The oblique arrows indicate two locations of Doppler sampling sites on the same segment of umbilical cord.