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©2013 UpToDate ® Print Email Doppler frequency shift waveforms depicting absent end-diastolic flow velocity in the umbilical artery As noted in the text, this is an ominous sign associated with adverse perinatal outcome. Note that the wall filter (high pass) was set very low (25Hz, upper right corner) in order to prevent any significant loss of the low frequency Doppler shifts thus ensuring against the artifactual appearance of absent end-diastolic velocity.