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
three 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
the left atrium. The ductus arteriosus moves blood from the pulmonary artery to the
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 three branches. The blood
reaches the inferior vena cava. This is a major vein connected to the heart. Most
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
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 mother's blood.