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.
The fetal part of the placenta is known as the chorion. The maternal component of the placenta is known as the decidua basalis.  Oxygen and nutrients in the maternal blood in the intervillous spaces diffuse through the walls of the villi and enter the fetal capillaries.