Britannica Sources used in this answer

How does progesterone prepare the uterus for pregnancy?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram of the menstrual cycle showing hormone levels, follicle development, and endometrial changes across 28 days. It highlights menstruation, ovulation, and the follicular and luteal phases, with labeled curves for estrogen, progesterone, FSH, and LH. — menstruation Cyclical changes during a woman's normal ovulatory menstrual cycle.

Progesterone plays a critical role in preparing the uterus for a potential pregnancy by inducing the secretory phase of the menstrual cycle.12

Following ovulation, the corpus luteum secretes progesterone, which causes the endometrial glands to become distended and tortuous while the stromal cells swell. This transformation makes the uterine lining receptive to a fertilized egg, allowing it to implant and begin development.12

Additionally, progesterone inhibits muscular contractions of the uterus that could otherwise cause the wall to reject an adhering egg. If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone levels; this withdrawal causes the uterine lining to break down and be shed during menstruation.12