Single umbilical artery: analysis of Doppler flow indices and arterial diameters in normal and small-for-gestational age fetuses

In this study we examined the value of Doppler flow measurements of the umbilical artery in distinguishing normal fetuses from those with single umbilical artery, and studied the Doppler flow differences and the compensatory arterial dilatation in appropriate (AGA) and small-for-gestational-age (SGA) fetuses with single umbilical artery. The Doppler flow indices (pulsatility index, S/D ratio) and the arterial diameters were prospectively and serially measured in 26 and 15 fetuses with single umbilical artery and without congenital malformations, respectively. Longitudinal changes in Doppler flow indices in normal and SGA fetuses with single umbilical artery are comparable, and are within normal reference ranges for three-vessel cords; there is a fairly constant widening of the single umbilical artery throughout gestation and a mean increase in size of about 1 mm over that found in normal cords from 20 weeks onward. In fetuses with single umbilical artery at mid-gestation, an umbilical artery diameter of more than 4 mm occurred in only 5/15 cases and is therefore not a reliable criterion for single umbilical artery screening prior to 26 weeks of gestation. Doppler flow measurements in normal and SGA fetuses with single umbilical artery are not significantly different from normal fetuses. Compensatory arterial dilatation may prevent fetuses with single umbilical artery from becoming growth retarded.