End-diastolic Umbilical Artery Doppler Flow Velocity

Doppler velocity measurement has been extensively applied in prenatal diagnosis for more than two decades. Blood flow in numerous vessels has been investigated to predict fetal condition, especially in the umbilical artery [1–7]. Histopathologic studies suggest that abnormal umbilical artery Doppler velocimetry is correlated with a pathologic lesion of the placenta characterized by obliteration of arterioles in the tertiary stem villi; the umbilical artery flow velocity waveform is primarily determined by placental villous vascular architecture [8,9]. The increased placental vascular resistance is reflected as a decreased diastolic phase of the umbilical artery waveform; moreover, end-diastolic flow of the umbilical artery vanishes and ultimately reverses in the progressively worsened condition, and absent or reversed enddiastolic velocity (AREDV) flow is finally present in the Doppler waveform [3,4,10,11]. AREDV during pregnancy is a strong indication of placental insufficiency. Previous studies have clarified that an increased umbilical artery systolic/diastolic ratio is a significant risk factor for progression of fetal acidosis, fetal distress, preterm delivery, low Apgar scores, and even perinatal death [12–15]. Mortality and morbidity (such as intraventricular hemorrhage [IVH], periventricular leukomalacia [PVL], bronchopulmonary dysplasia [BPD], respiratory distress syndrome [RDS], necrotizing enterocolitis [NEC], and long-term neurodevelopmental impairment) of fetuses with AREDV in the umbilical artery have been well discussed, especially in growth-restricted fetuses [1,2,10,16,17]. When AREDV occurs prenatally, close follow-up or expeditious delivery should be considered. High-risk pregnancies, such as preeclampsia and intrauterine growth restriction (IUGR), have abnormal development of the placenta vasculature which can be revealed in the abnormal Doppler velocimetry [9,18]. THE EFFECTS OF ABSENT OR REVERSED END-DIASTOLIC UMBILICAL ARTERY DOPPLER FLOW VELOCITY