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Reversal of umbilical arterial end diastolic flow

Reversal of end diastolic flow (REDF) or velocity in umbilical arterial flow assessment is often an ominous finding if detected after 16 weeks. It is classified as Class III in severity in abnormal umbilical arterial Dopplers 6.


The estimated incidence is at ~0.5% of all pregnancies with a much higher rate in intrauterine growth restricted (IUGR) fetuses.


The feature is seen as a result of a signifcant increase in resitance in blood flow within the placenta and often represents a 'tip of the iceberg" where there is a much larger underlying pathology.

In a normal situation umbilical arterial flow should always be in the forward direction in both systole and diastole. 

However during the first 16 weeks a reversal in end diastolic flow can be a normal finding due to the low resistance arcuate arteries and inter villous spaces not yet being formed.

Flow reversal can also be detected in the fetal aorta.

Radiographic assessment

Ideally a low wall filter setting (<100Mhz) and an acute insonation angle of <30% is recommended 4.

The severity can be quanitified by the ratio of the maximum antegrade velocity (a) versus the maximum retrograde velocity (b).


It is associated with signifcant perinantal mortality (27-64% 1-3) and overall mortality >50% 1.

See also

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