Umbilical vein to artery ratio in fetuses with single umbilical artery

Abstract

In fetuses with single umbilical artery (SUA) the entire blood flow to the placenta is transported through only one umbilical artery, resulting in a compensatory increase of the arterial diameter. In order to establish whether umbilical vessel size could be used as an additional ultrasonographic criterion for prenatal diagnosis of SUA, we measured umbilical vein and umbilical artery diameters in 55 fetuses with SUA and in 55 with a normal three-vessel cord matched for gestational age. In all but one fetus with SUA, the diameter of the umbilical artery was greater than 50% of that of the umbilical vein, resulting in an umbilical vein to umbilical artery ratio of < or = 2. In contrast, none of the fetuses with a three-vessel cord had a ratio of < or = 2. Increasing diameter of the umbilical artery with no modification of the diameter of the vein is a characteristic prenatal ultrasonographic feature of SUA, making this observation a useful technique for the detection of this vascular anomaly in utero.

Volumetric umbilical artery blood flow: comparison of the normal versus the single umbilical artery cord

“…This was initially performed with gray scale 22 and later, with improved accuracy, with the addition of color Doppler 23,24 . Transverse or longitudinal views of the cord may demonstrate the SUA, but it was the identification of the course of the umbilical arteries around the bladder that confirmed the diagnosis 3,6,25,26 . This later technique with color Doppler was utilized in all of our cases.…”

“…The technique to measure the umbilical artery diameter has been described 25,27,28 as the inner diameter on enlarged views of the cord, either in transverse or longitudinal plane. We took care to avoid fetal breathing, which may alter the flow through the vessel, as well as averaging two or three measurements to decrease the risk of error, including pulsatility of the vessel wall.…”

“…The fact that their measurements were somewhat smaller may be due to the fact that they studied the cord as it entered the abdominal wall. It has been shown that the SUA undergoes a compensatory increase in diameter over the two-artery cord 25,28,29 . In vitro techniques by some authors found the SUA to be 1.5 times larger than the normal artery 29 , while others 28 found that, after 20 weeks' gestation, the artery in the SUA was at least 1 mm larger than the normal artery.…”

Sonographic findings of the umbilical cord: implications for the risk of fetal chromosomal anomalies

“…Increased diameter of the umbilical artery or similar diameters of the artery and the vein are also sonographic features characteristic of SUA ( Figure 1). It has been suggested that a transverse diameter of the umbilical artery larger than 4 mm or an umbilical vein to artery ratio ≤ 2 is predictive of SUA 16,17 . However, the limitations and pitfalls of such cutoff measurements in the sonographic diagnosis of SUA were recently pointed out 18 .…”

Should fetal growth be a matter of concern in isolated single umbilical artery?

“…Compensatory mechanisms allow increase in blood flow through the single artery in order to meet the demands of fetal growth and development throughout pregnancy. 3 Although several studies have reported diminished fetal growth in these pregnancies, [4][5][6][7][8][9][10][11][12] others have not shown differences. [13][14][15] These contradictory findings may be attributed to diverse methodological differences in the published literature.…”