Fetal Circulation and Physiological Changes at Birth

Overview of Fetal Circulation

Fetal circulation is uniquely designed to bypass the lungs, as oxygenation occurs via the placenta. The circulatory system is adapted to direct oxygen-rich blood to vital organs while minimizing pulmonary blood flow.

Key Structures in Fetal Circulation

• Placenta: Provides oxygen and nutrients to the fetus.
• Umbilical Vein: Transports oxygenated blood from the placenta to the fetal liver and ductus venosus.
• Ductus Venosus: Shunts oxygenated blood from the umbilical vein to the inferior vena cava.
• Foramen Ovale: A pathway allowing blood to flow between the right and left atrium to bypass the lungs.
• Ductus Arteriosus: Diverts blood away from the pulmonary circulation by connecting the pulmonary artery to the descending aorta.

Physiological Changes at Birth

At birth, dramatic circulatory adjustments occur as the newborn transitions to independent respiration. Key changes include:

• Closure of the ductus venosus, foramen ovale, and ductus arteriosus.
• Increased pulmonary circulation and lung expansion.
• Functional remodeling of cardiac pressures and blood flow.

Clinical Implications

Defects in fetal circulatory adaptation can lead to congenital conditions such as patent ductus arteriosus and atrial septal defects, necessitating medical intervention.