[Vascular diameter and resistance indices in normal fetuses with a single umbilical artery]

This study was undertaken to investigate the vascular-adaptive mechanism of fetuses with a single umbilical artery (SUA) and without structural anatomical abnormalities.

A cohort study including fetuses with the diagnosis of SUA at routine ultrasonographic examination was designed. The diagnosis of SUA was confirmed by color Doppler imaging and by histological examination of the umbilical cord after delivery. The inner artery and vein diameters were measured and the resistance-index (RI) of the SUA was calculated.

Eleven fetuses were studied. The artery and vein diameters were 2 standard deviations above the mean, when plotted in reference ranges, in 12 out of 17 (70.5%) and 8 out of 16 (50%) measurements, respectively. The RI-values were below the 5th and 50th percentile in 50% (6/12) and 75% (9/12) of the measurements, respectively.

A dilatation of the single artery occurs to reduce the impedance in this vessel and to preserve a sufficient feto-placental blood flow. In addition the umbilical vein also increases in size.