In fetal circulation, the ductus venosus bypasses the liver and the ductus arteriousus bypasses the lungs. Ductus arteriosus also called ductus botalli is a blood vessel connecting the main pulmonary artery to the proximal ascending aorta. It does allow most of the blood from right ventricle to bypass the fetus's fluid-filled non-functioning lungs. Ductus venosus on the hand allows oxygenated blood from the placenta to bypass the liver.
