Definition
- At birth, cord clamping abolishes umbilical blood flow and triggers circulatory and respiratory changes that convert fetal circulation into the adult postnatal pattern.
- Before birth, fetal lungs are functionally inactive and gas exchange occurs via the placenta; umbilical venous blood is only about 80% saturated with oxygen.
Fetal Circulation: Shunts and Oxygenation
- Placenta functions as the fetal lungs; oxygenated blood reaches the fetus through the umbilical vein.
- Three shunts bypass the fetal liver and lungs:
- Ductus venosus: into inferior vena cava.
- Foramen ovale: right atrium to left atrium.
- Ductus arteriosus: pulmonary artery to aorta.
Fetal circulation, schematic diagram