I. Ductus venosus and inferior vena cava blood flows during normal pregnancy

Abstract

Objective: To compare dynamic of S/D ratio in ductus venosus (DV) with one in inferior vena cava (IVC) during normal pregnancy.

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Methods: Blood flow waveforms in the D V and IVC were recorded in 162 fetuses from normal pregnancies between 9 and 40 weeks of gestation (Aloka 2000). Peak systolic (S) diastolic (D) velocities of blood flow waveforms and S/D ratio were measured.

Results: DV S/D ratio decreased as a function of increasing gestational age [SD = 1,721 — 0,231 x (week’s gestation) + 0,07 x (week’s gestation), p<0,0001]. This was attributed to an increase in the velocity of D wave. IVC S/D ratio increased with advancing gestational age [SD = 1,628 + 0,0018 x (week’s gestation)²; p<0,002] because of the increasing in the velocity of S wave.

Conclusions: Experimental studies have shown that inferior vena cava blood passes through the right atrium mainly to the right ventricle. Ductus venosus blood, which contains well-oxygenated umbilical blood, passes through the foramen ovale to the left atrium and left ventricle. Thus, S and D wave of DV waveforms could reflect the hemodynamic status of the left ventricle whereas S and D wave IVC waveforms could reflect the hemodynamic status of the right ventricle. Our findings have suggested that compliance of the right ventricle could be different from left one.