Fetal Circulation

Since the lungs are not used in the fetus (because oxygenated blood comes from the umbilical vessels), blood is shunted around in different ways:
0. Umbilical vessels
Umbilical arteries drains blood from fetal iliac arteries; blood is passed through vessels in the placenta and diffusion between it and the mother's blood can occur, thus delivering nutrients to the fetus and removing wastes. The umbilical vein returns oxygenated blood to the liver (half of which will go through the liver and the other half through the DV)
1. Ductus venosus
This structure bypasses the liver and joins with the IVC to direct oxygenated blood from umbilical vessels to heart and thus the rest of the circulation.
2. Foramen ovale

Since RA receives oxygenated blood (from IVC/DV/Umbilicus), and that the lungs do not supply oxygen at this time, there is a hole between the atria that allows blood to travel from RA to LA so oxygenated blood can be delivered to other systems. The Septum primum on the left side prevents blood going from left to right.

3. Ductus arteriosus
Similar to the foramen ovale, this allows blood to flow between the pulmonary trunk and the aorta.