Fetal CirculationHow does the fetal circulatory system work? During pregnancy, the fetal circulatory system works differently than after birth:

The fetus is connected by the umbilical cord to the placenta, the organ that develops and implants in the mother's uterus during pregnancy. Through the blood vessels in the umbilical cord, the fetus receives all the necessary nutrition, oxygen, and 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 eliminated.

Blood from the mother enters the fetus through the vein in the umbilical cord. It goes to the liver and splits into three branches. The blood then reaches the inferior vena cava, a major vein connected to the heart. Inside the fetal heart:

Blood enters the right atrium, the chamber on the upper right side of the heart. Most of the blood flows to the left side through a special fetal opening between the left and right atria, called the foramen ovale. Blood then passes into the left ventricle (lower chamber of the heart) and then to the aorta, (the large artery coming from the heart). From the aorta, blood is sent to the head and upper extremities. After circulating there, the blood returns to the right atrium of the heart through the superior vena cava. About one-third of the blood entering the right atrium does not flow through the foramen ovale, but, instead, stays in the right side of the heart, eventually flowing into the pulmonary artery.

Because the placenta does the work of exchanging oxygen (O2) and carbon dioxide (CO2) through the mother's circulation, the fetal lungs are not used for breathing. Instead of blood flowing to the lungs to pick up oxygen and then flowing to the rest of the body, the fetal circulation shunts (bypasses) most of the blood away from the lungs. In the fetus, blood is shunted from the pulmonary artery to the aorta through a connecting blood vessel called the ductus arteriosus.

Blood circulation after birth: With the first breaths of air the baby takes at birth, the fetal circulation changes. A larger amount of blood is sent to the lungs to pick up oxygen.

Because the ductus arteriosus (the normal connection between the aorta and the pulmonary valve) is no longer needed, it begins to wither and close off. The circulation in the lungs increases and more blood flows into the left atrium of the heart. This increased pressure causes the foramen ovale to close and blood circulates normally.

Adult Derivatives of Fetal Vascular Structures Because of certain changes in the cardiovascular system at birth, certain vessels and structures are no longer required. Over a period of months these fetal vessels form nonfunctional ligaments, and fetal structures such as the foramen ovale persist as anatomic vestiges of the prenatal circulatory system. Fetal Structure Foramen Ovale Umbilical Vein (intra-abdominal part) Ductus Venosus Umbilical Arteries and abdominal ligaments Ductus Arteriosum Fossa Ovalis Ligamentum teres Ligamentum venosum Medial umbilical ligaments, superior vesicular artery (supplies bladder) Ligamentum arteriosum Adult Structure

Two common defects:1. patent ductus arteriosus common in females 2-3 times more than males, unknown reason why If instead of functional closure after birth there is patent structure then aortic blood is shunted into the pulmonary artery. Most common congenital anomaly associated with maternal rubella infection during early pregnancy (mode of action by virus unclear) Premature infants usually have a PDA due to hypoxia and immaturity. Surgical closure of PDA is achieved by ligation and division of the DA. 2. Patent foramen ovale most common form of an Atrial Septal Defects (ASDs) a small isolated patent foramen ovale is of no hemodynamic significance; but if other defects present (e.g. pulmonary stenosis or atresia), blood is shunted through the foramen ovale into the left ventricle, producing cyanosis, a dark bluish coloration of the skin and mucous membranes resulting from deficient oxygenation of the blood. A probe patent foramen ovale is present in up to 25% of people. A probe can be passed from one atrium to the other through the superior part of the floor of the fossa ovalis. Though not clinically significant (usually small) but may be forced open because of other cardiac defects and contribute to functional pathology of the heart. Results from incomplete adhesion between the original flap of the valve of the foramen ovale and the septum secundum after birth.