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Introduction

Fetal circulation differs considerably from adult circulation in that oxygen is supplied to the fetus by the mother's placenta, no gas exchange occurs in the fetal lungs, and the majority of blood is directed away from nonfunctional organs (eg, lungs) to vital structures (eg, brain, heart).

Specialized fetal structures

The fetal circulatory system contains 5 structures that are not normally patent in the adult.  These include:

  • Umbilical arteries (2) ( Figure 1):  Transport deoxygenated blood from the fetus to the placenta.
  • Umbilical vein:  Transports oxygenated blood from the placenta to the fetus.
  • Ductus venosus:  Connects the umbilical vein to the inferior vena cava, bypassing the liver and shunting blood into the inferior vena cava and toward the heart.
  • Foramen ovale:  Shunts oxygenated blood from the right atrium to the left atrium.

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