The baby’s lungs have no ventilation function in the womb, and there is no breathing in the traditional sense. The survival and development of the body depend on the umbilical cord blood, and the oxygen in the body is provided through the umbilical cord blood. When the fetus is in the mother’s body, the lungs are not open and do not have respiratory function. When the fetus is in the mother’s body, it is connected to the mother’s blood system through the umbilical cord. The mother produces arterial blood through breathing, and the hemoglobin in the arterial blood combines with abundant oxygen, and enters into the circulation of the fetus through the umbilical cord, and completes internal respiration in the body of the fetus. That is, the oxygen in the arterial blood is exchanged with the carbon dioxide in the tissue cells to maintain the tissue cells containing sufficient oxygen. Therefore, when the baby is inside the mother’s body, the oxygen in the baby’s body comes exclusively from the arterial blood produced by the mother’s respiration.