Now, there are two important purposes. Firstly, it basically stimulates the corpus luteum found in the ovary to release progesterone and estrogen until the placenta can actually take over that job and begin releasing these hormones on its own. And this is required to basically maintain the development of the endometrium during the process of pregnancy. It also acts to actually suppress the immune system of the mother. So remember, what the immune system does is it basically attacks any foreign object that is found inside our body. And technically speaking, the fetus as well as our placenta are two foreign objects.