Fetal Circulation

Definition - What does Fetal Circulation mean?

Fetal circulation is an umbrella term for the circulatory system (through which blood and lymph flow throughout the body of the unborn baby and comprises of heart, blood vessels, blood, and lymph) and the placental system (which includes the birth cord and the blood vessels in the placenta that carry blood to and from the fetus). The circulation in the baby before birth functions in a distinct manner than the circulation after birth. This is because the lungs are not working in the fetus. Instead, the work of the lungs is performed by the mother (via the placenta and the umbilical cord), who delivers oxygen and nutrients to the fetus. At birth, when an infant takes a breath and the umbilical cord is cut, the fetal circulation is transformed into the adult-like circulation with functioning lungs.

FertilitySmarts explains Fetal Circulation

The placenta receives oxygen-lacking blood (blue-colored blood) from the fetus through the blood vessels (the two umbilical arteries) that leave the fetus to travel through the umbilical cord. On reaching the placenta, the blue blood accepts oxygen and turns red. From the placenta, this oxygen and nutrient-rich red blood then traverses via a third vessel in the umbilical cord (called the umbilical vein) to the fetus. On entering the fetus, the red blood can take a turn through two different routes. It can travel through the fetal liver to enter the right side of the heart, or otherwise, less than a third is channeled through another vein to bypass the liver. This shunted blood enters the right side of the heart via one of the great veins of the heart.

What happens to the blood after entering the right side of the heart? It navigates through one of the two connections in the fetal heart that will close after birth.

First connection: There is a hole between the upper two heart chambers (right and left atria), referred to as a patent foramen ovale (PFO). PFO enables most of reddest blood to flow from the right atrium into left atrium, thus bypassing the lungs. From the left atrium, the blood goes into the lower left chamber (left ventricle) and out from the left side of the heart into the aorta.

Second connection: Alternatively, some of the blue blood entering the right atrium from the fetus's body does not pass directly to the left atrium through the foramen ovale, but enters the lower right heart chamber (right ventricle -the chamber that normally pumps blood to the lungs via a vessel called pulmonary artery after the baby is born). However, in the fetus most of the blood that leaves the right ventricle is not carried to the lungs; instead, it bypasses the lungs through the second of the two additional fetal connections known as the ductus arteriosus. The ductus arteriosus that connects the pulmonary artery to the aorta also delivers the blue blood to the organs in the lower half of the fetal body. This blue blood then departs from the fetus's body to get back to the placenta (by way of the umbilical arteries) to pick up oxygen again, and hence, the above cycle is repeated.

An sassessment of the amount of forward blood flow through the umbilical artery allows for an overall measure of fetal health. The two shunts (PFO and PDA) in the fetal circulation are critical to the survival of the fetus even with complicated heart defects. They should, however, close after birth.

Potential issues related to fetal circulation include:

Patent Ductus Arteriosus: If the ductus arteriosus fails to close after birth, it can lead to a left-to-right shunting of blood. This compromises the baby's heart and lungs, and in long-standing cases, can lead to bleeding within the brain.

ingle Umbilical Artery (SUA): Occasionally, the umbilical cord contains only one umbilical artery, instead of the normal two. Most of the times, an SUA doesn't cause any significant problems. However, in 25% of children, an SUA accentuates the chances of developing cardiac, bone, intestinal or kidney problems.

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