日本小児循環器学会雑誌 Pediatric Cardiology and Cardiac Surgery

A characteristic of fetal circulation is that the relationship between the right and left ventricles is parallel, with one intracardiac shunt (foramen ovale) and two unexpected shunts (ductus venosus and ductus arteriosus) in which lung circulation is not established and fetal oxygen is supplied from the placenta. The main blood flow streams from the right ventricle toward the descending aorta through the main pulmonary artery and ductus arteriosus, with little blood circulating in the lungs. Therefore, an evaluation of the right heart system, including the placenta and three shunts, is important for determining the cardiac function of the fetus. Until the third trimester of pregnancy, the pulmonary blood flow increases to four times that in the first trimester, and left ventricle blood flow that normally bears 45% of the total cardiac output in fetal circulation increases 2–3 times after birth. It is important to understand the characteristics of fetal circulation and its dramatic transition to the postnatal circulation to delineate the pathophysiology of congenital heart diseases.