Answer:
the build up of endometrium
Step-by-step explanation:
Progesterone begins to occur after a woman's puberty, once she has had her first period. From then on, it will occur in each menstrual cycle and will gradually deteriorate until the woman has menopause. In this way, progesterone also helps the development of secondary sexual characteristics of women.
Once ovulation occurs during the menstrual cycle, the ovaries will start producing progesterone. Progesterone then acts on the endometrium, and causes it to secrete special proteins that nourish the fertilized egg, providing optimal conditions for the development of the embryo. After ten weeks of pregnancy, it will be the placenta that is responsible for producing progesterone to maintain adequate levels and make the pregnancy develop safely.
If the ovum has not been fertilized but progesterone has been released, the excess of this hormone that the body does not need will be expelled with the rest of the menstruation.