Progesterone is a female hormone secreted by the corpus luteum in the ovary. It stimulates proliferation of the lining of the uterus for implantation of an embryo. Once embryonic implantation does occur, progesterone continues to be secreted by the corpus luteum and subsequently by the placenta. This maintains the pregnant uterus and prevents further release of eggs from the ovary. It is also responsible for development of milk-secreting cells in the breasts.
PROGESTERONE: "Levels of progesterone are as much as 10x higher in pregnant women than those not so."