Blood Circulation in the Fetus and Newborn

How does the fetal circulatory system work?





Illustration of blood flow, or circulation, in a fetus.
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Inside the fetal heart:



  • From the aorta, blood is sent to the heart muscle itself in addition to the brain. After circulating there, the blood returns to the right atrium of the heart through the superior vena cava. About  two thirds of the blood will pass through the foramen ovale as described above, but the remaining one third will pass into the right ventricle, toward the lungs. 

  • In the fetus, the placenta does the work of breathing instead of the lungs. As a result, only a small amount of the blood continues on to the lungs. Most of this blood is bypassed or shunted away from the lungs through the ductus arteriosus to the aorta. Most of the circulation to the lower body is supplied by blood passing through the ductus arteriosus. 




Illustration of the anatomy of the heart, normal
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