Placental Function and Adaptations to Exercise

The Placenta is an organ that develops during pregnancy, it functions to maintain the transport of oxygen and carbon dioxide between the mother and the baby. It basically serves as the baby's lung. It is highly vascularized; small blood vessels carrying the baby's blood run through the placenta which is full of the mother's blood. Nutrients and oxygen from the mother's blood and transferred to the baby's blood, and waste products (including CO2) are transferred from the baby's blood to the mother's blood so that her body can get rid of it. Although not relevant to the discussion of exercise, it is important to note that the mother and the baby's blood never actually mix, the baby has it's own blood separate and individually unique from the mother's. 
The following information also comes from my book "Exercising Through your Pregnancy." Dr. James F. Clapp found that regular exercise has some positive effects on the growth and function of the placenta that help to protect the fetus from oxygen deprivation. "The placentas of women who exercise regularly throughout early and mid-pregnancy grow faster and function better that those of women who are healthy but don't exercise regularly. This means that at any rate of uterine blood flow, more oxygen and nutrients can get across to the baby of a woman who exercises than to the baby of one who does not. This probably is not important under most circumstances,  because unless there is a problem or a large decrease in flow (as during hemorrhage or strenuous exercise), both placentas will supply the baby adequately."