UMBILICAL VEIN TO ARTERY RATIO IN FETUSES WITH SINGLE UMBILICAL ARTERY

In fetuses with single umbilical artery (SUA) the entire blood flow to the placenta is transported through only one umbilical artery, result ing in a compensatory increase of the arterial diameter. In order to e stablish 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 a nd 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 wa s greater than 50% of that of the umbilical vein, resulting in an umbi lical vein to umbilical artery ratio of less than or equal to 2. In co ntrast, none of the fetuses with a three-vessel cord had a ratio of le ss than or equal to 2. Increasing diameter of the umbilical artery wit h no modification of the diameter of the vein is a characteristic pren atal ultrasonographic feature of SUA, making this observation a useful technique for the detection of this vascular anomaly in utero.