Chapter 2:

Fetal Circulation

In utero, the prenatal circulation depends heavily on the mother's circulation system for survival and development. During development, fetal nutrition, oxygenated blood, excretion, respiration and protection are provided by the placenta. Development begins when the blastocyst attaches itself somewhere near the upper portion of the uterine cavity. Diffusion of substances between maternal and fetal blood occurs in the intervillous space created there.

While the ductus venosus and foramen ovale rarely cause problems at birth, if the ductus arteriosus does remain patent or reopens in response hypoxia, this can lead to problems. If fetal circulation is maintained it can lead to a massive shunt causing hypoxia and pulmonary hypertension. The normal newborn % shunt of 20 to 25% is much higher in the presence of a patent ductus arteriosus.