Objective: Our objective was to establish reference values for ductus venosus, inferior vena cava and hepatic vein flow velocities during ventricular systole (S-wave) and diastole (D-wave), the lowest forward velocity during atrial contraction (a-wave), the intensity-weighted mean flow velocity (Vmean) and different calculated indices.
Methods: Venous flow velocity waveforms were obtained from 329 singleton pregnancies at 20-42 weeks of gestation by pulsed-wave color Doppler. Reference values were constructed by means of a quadratic regression model after logarithmic transformation of original data.
Results: With advancing gestational age the peak velocity index for the vein (PVIV) and pulsatility index for the vein (PIV) decreased whereas blood flow velocities increased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic vein. Values for PVIV and PIV were highest in the hepatic vein and lowest in the ductus venosus. During atrial contraction there was a blood flow towards the fetal heart in the ductus venosus, whereas in the inferior vena cava and in the hepatic vein blood flow was either in the opposite from the fetal heart (reverse flow), or there was absent flow (zero flow) or flow was towards the fetal heart (positive flow).
Conclusions: The reference ranges and calculated velocities established in this study may be utilized in studies dealing with the role of ductus venosus and inferior vena cava blood flow in fetuses with chromosomal abnormalities or congenital heart disease as well as hypoxic conditions. We speculate, that the reduction in PVIV and PIV with advancing gestational age may reflect a decrease in cardiac afterload as a result of maturation of diastolic ventricular function.