Most of what I know with fasting is that for health benefits, it causes autophagy, which leads to all the health benefits. Essentially (in lay-mens terms), autophagy is when the cells recycle because you are not eating nutrients. They are using the stuff within the cells to create the energy they need to operate.
What does the placenta do? The placenta is an organ that develops in your uterus during pregnancy. This structure provides oxygen and nutrients to your growing baby and removes waste products from your baby's blood. The placenta attaches to the wall of your uterus, and your baby's umbilical cord arises from it. In most pregnancies, the placenta attaches at the top or side of the uterus. Various factors can affect the health of the placenta during pregnancy, some modifiable and some not. For example: Maternal age.
Further information: Placenta. In placental mammals, the placenta forms after the embryo implants into the wall of the uterus. The developing fetus is connected to it via an umbilical cord. Animal placentas are classified based on the number of tissues separating the maternal from the fetal blood. The placentation types found in animals are: