Estrogen and Progesterone function like a complex symphony working together to keep our bodies (and fertility) in a state of balance.
Progesterone is the dominant hormone in the second half or luteal phase of your menstrual cycle, and its role is to continue the work of estrogen in preparing the lining of your uterus for pregnancy*
If the egg you released is fertilized by a sperm + you become pregnant, the corpus luteum continues to produce progesterone until about 10 weeks of pregnancy. Then, your placenta takes over. If you do not become pregnant, then your corpus luteum dissolves, your progesterone levels drop, you get your period, and a new menstrual cycle begins.