The fetal circulation is a completely unique system The fetal circulation is otherwise known as the placental circulation. It is in the placenta where the exchange of substances between the blood of the fetus and the mother's blood takes place. We won't describe the whole system - this subject is complicated even for medical students😁 But here's an interesting fact - the blood of the mother and fetus do not mix. While in utero, the heart of a 12-week-old fetus pumps 28 liters of blood per day, at this time the frequency of its beats is almost 2 times higher than that of an adult.