UMBILICAL VESSEL DIAMETER AND RESISTANCE INDEXES IN NORMAL FETUSES WITH SINGLE UMBILICAL ARTERY

This study was undertaken to investigate the vascular-adaptive mechani sm of fetuses with a single umbilical artery (SUA) and without structu ral anatomical abnormalities. Methods: A cohort study including fetuse s with the diagnosis of SUA at routine ultrasonographic examination wa s designed. The diagnosis of SUA was confirmed by color Doppler imagin g 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. Results: Eleven fetuses were st udied. The artery and vein diameters were 2 standard deviations above the mean, when plotted in reference ranges, in 12 out of 17 (70.5%) an d 8 out of 16 (50%) measurements, respectively. The RI-values were bel ow the 5th and 50th percentile in 50% (6/12) and 75% (9/12) of the mea surements, respectively. Conclusion: A dilatation of the single artery occurs to reduce the impedance in this vessel and to preserve a suffi cient feto-placental blood flow. In addition the umbilical vein also i ncreases in size.