According to the literature, oxygenated blood from the ductus venosus and hepatic veins may either enter the right atrium before flowing through the foramen ovale to the left atrium, or flow directly from the ductus venosus and the hepatic veins to the foramen ovale, bypassing the right atrium. To address this problem, 103 normal fetuses were examined by two-dimensional imaging, M-mode and color Doppler at an average gestational age of 27 weeks (range, 15-40 weeks). The position of the ventricular septum and foramen ovale, and the angle and flow direction of the inferior vena cava, ductus venosus and hepatic veins were recorded. Two pathways for blood were described: a left ductus venosus-foramen ovale pathway that delivers blood directly to the foramen ovale circumventing the right atrium, and a right inferior vena cava-right atrium pathway that delivers blood into the right atrium through the right portion of the proximal inferior vena cava at an angle of 13 degrees to the long axis of the spine. The left and medial hepatic veins enter the left ductus venosus-foramen ovale pathway, and the right hepatic vein enters the right inferior vena cava-right atrium pathway. This supports the hypothesis that oxygenated blood from the ductus venosus and left hepatic veins flows directly through the foramen ovale to the left atrium avoiding extensive mixture in the inferior vena cava and an intermediate entrance to the right atrium.
Copyright 1992 International Society of Ultrasound in Obstetrics and Gynecology