During pregnancy, the fetal circulatory system works differently than after birth:
The fetus is connected by the umbilical cord to the placenta. This is the organ that
develops and implants in the mother's uterus during pregnancy.
Through the blood vessels in the umbilical cord, the fetus gets all needed nutrition
and oxygen. The fetus gets life support from the mother through the placenta.
Waste products and carbon dioxide from the fetus are sent back through the umbilical
cord and placenta to the mother's circulation to be removed.
The fetal circulatory system uses 3 shunts. These are small passages that direct blood
that needs to be oxygenated. The purpose of these shunts is to bypass the lungs and
liver. That's because these organs will not work fully until after birth. The shunt
that bypasses the lungs is called the foramen ovale. This shunt moves blood from the
right atrium of the heart to the left atrium. The ductus arteriosus moves blood from
the pulmonary artery to the aorta.
Oxygen and nutrients from the mother's blood are sent across the placenta to the fetus.
The enriched blood flows through the umbilical cord to the liver and splits into 3
branches. The blood then reaches the inferior vena cava. This is a major vein connected
to the heart. Most of this blood is sent through the ductus venosus. This is also
a shunt that lets highly oxygenated blood bypass the liver to the inferior vena cava
and then to the right atrium of the heart. A small amount of this blood goes straight
to the liver to give it the oxygen and nutrients it needs.
Waste products from the fetal blood are transferred back across the placenta to the