The nutritional supply of the fetus and the excretion of metabolites are transmitted by the placenta and umbilical cord to the mother. The foramen ovale is precisely such a special structure. The foramen ovale is located between the left and right atria of the fetus, and its opening faces the entrance of the fetal inferior vena cava, so that most of the blood entering the right atrium of the fetus from the inferior vena cava passes through the foramen ovale into the left atrium of the fetus. After birth, the foramen ovale begins to close due to the increased pressure in the left atrium, and most of them close completely around 6 months after birth.