Role of ductus venosus in distribution of umbilical blood flow in human fetuses during second half of pregnancy

Color Doppler sonography was used to study umbilical and ductus venosus (DV ) flow in 137 normal fetuses between 20 and 38 wk of gestation. Hepatic flo ws were also evaluated. In all parts of the venous circulation examined, bl ood flow increased significantly with advancing gestational age. The weight -specific amniotic umbilical flow did not change significantly during gesta tion (120 +/- 44 ml.min(-1).kg(-1)), whereas DV flow decreased significantl y (from 60 to 17 ml.min(-1).kg(-1)). The percentage of umbilical blood flow shunted through the DV decreased significantly (from 40% to 15%); conseque ntly, the percentage of flow to the liver increased. The right lobe flow ch anged from 20 to 45%, whereas the left lobe flow was approximately constant (40%). These changes are related to different patterns of growth of the um bilical veins and DV diameters. The present data support the hypothesis tha t the DV plays a less important role in shunting well-oxygenated blood to t he brain and myocardium in late normal pregnancy than in early gestation, w hich leads to increased fetal liver perfusion.