Blood flow and the degree of shunting through the ductus venosus in the human fetus

OBJECTIVES: Our goal was to determine the degree of shunting through the ductus venosus in the human fetus and its possible association with fetal growth. STUDY DESIGN: Blood flow in the umbilical vein and the fetal ductus venosus was measured in 197 low-risk pregnancies in a cross-sectional ultrasonographic study at a gestational age of 18 to 41 weeks. The degree of shunting was compared to birth weight and ponderal index. RESULTS: The average fraction shunted through the ductus venosus was 28% to 32% at 18 to 20 weeks, decreased to 22% at 25 weeks, and reached 18% at 31 weeks (with wide ranges expressed in the 10th and 90th percentiles). Fetuses <10th percentile for birth weight had significantly more shunting (1.4%) than those >90th percentile (95% confidence interval, 0.1%-2.7%; P=.04). CONCLUSIONS: In the human fetus a higher proportion of umbilical blood is directed to the liver and less is shunted through the ductus venosus, in comparison with what has previously been shown in animal experiments.