The fluid dynamics in the human fetal ductus venosus in the early stage of pregnancy is not well explored. Consequently, there is an uncertainty in the interpretation of the temporal and spatial velocity variation in the ductus venosus. A robust estimation procedure for non-invasive measurement of the blood flow, based on conventional Doppler ultrasound measurements, is therefore missing. The aim of the present study was to describe the spatial and temporal velocity distribution at the ductus venosus bifurcation for boundary condition typical for fetuses at 11-13 weeks of gestation by means of a mathematical model. In particular we wanted to investigate velocity profiles at the ductus venosus inlet region in early pregnancy under normal conditions, to assess whether robust estimates of velocity profile shape coefficients may be given in order to provide noninvasive volumetric flow rate assessment in the ductus venosus. Such information will be useful in a clinical assessment of the fetus. Our model predicted a close to parabolic velocity profile in the inlet section of the ductus venosus during the cardiac cycle, with a shape factor of 0.53. Our simulations also showed that during atrial contraction (the A-wave), transient simultaneous positive and negative velocities may be observed in the same cross-section, in Womersley-like velocity profiles. Thus, as previous clinical investigators have reported these velocities as either positive or negative, our findings challenge clinical interpretation.
Keywords: Ductus venosus; First trimester; Velocity profiles.