Fetal circulation differs significantly from postnatal circulation because the fetal lungs do not function for gas exchange. Instead, the placenta provides oxygen and removes carbon dioxide. Three unique structures facilitate this arrangement: the ductus venosus shunts oxygen-rich blood from the umbilical vein past the liver to the heart, the foramen ovale allows blood to pass directly from the right atrium to the left atrium, and the ductus arteriosus diverts blood from the pulmonary artery to the aorta, bypassing the lungs. Understanding fetal circulation is essential for interpreting fetal Doppler studies and fetal echocardiography, as the expected flow patterns in fetal vessels are very different from those in postnatal life.
Sonography Term