Reversal of umbilical arterial end diastolic flow

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

Epidemiology

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

Pathology

The feature is seen as a result of a significant increase in resistance to 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 intervillous spaces not yet being formed.

Flow reversal can also be detected in the fetal aorta.

Radiographic features

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

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

Treatment and prognosis

It is associated with significant perinatal mortality (27-64% ^1-3) and overall mortality >50% ¹.

See also

• absent umbilical arterial end-diastolic flow