Fetal Circulation and Physiological Changes at Birth

Introduction

Fetal circulation is uniquely adapted to support the developing fetus. The transition from intrauterine to extrauterine life involves significant physiological changes, including the closure of fetal shunts.

Fetal Circulation

Before birth, fetal circulation differs significantly from neonatal circulation. Oxygenated blood is supplied by the placenta and distributed through specialized shunts:

Ductus Venosus: Allows oxygen-rich blood to bypass the liver and flow directly into the inferior vena cava.
Foramen Ovale: A shunt between the right and left atria, enabling oxygen-rich blood to bypass the lungs.
Ductus Arteriosus: Diverts blood from the pulmonary artery to the aorta, preventing excessive blood flow to the underdeveloped fetal lungs.

Physiological Changes at Birth

After birth, major adaptations occur:

Closure of Foramen Ovale: Increased pulmonary circulation and left atrial pressure lead to the functional closure of the foramen ovale.
Closure of Ductus Arteriosus: Elevated oxygen levels and reduced prostaglandins facilitate its closure.
Closure of Ductus Venosus: With the cessation of placental circulation, the ductus venosus undergoes functional closure.

Neonatal Adaptations

The transition to neonatal circulation ensures proper oxygenation and nutrient distribution. Lung expansion initiates pulmonary blood flow, and systemic circulation stabilizes.