How do estrogen and progesterone prepare the uterus for implantation?

Estrogen and progesterone, which are steroid hormones, work in tandem to prepare the endometrium (the inner lining of the uterus) for the implantation of a fertilized ovum.123

The preparation occurs through the distinct phases of the menstrual cycle:

• Proliferative Phase: Driven by increasing levels of estrogen, the endometrium proliferates and thickens following menstruation.43
• Secretory Phase: Following ovulation, the corpus luteum secretes large quantities of progesterone. This hormone stimulates the endometrium to enter a state of active secretion, making the lining receptive to the attachment and embedding of the blastocyst.1342

Additionally, progesterone inhibits muscular contractions of the uterus that could otherwise cause the wall to reject the adhering egg. If fertilization occurs, the resulting embryo signals the continued production of progesterone, which maintains the endometrium and prevents the onset of menstruation, thereby supporting the early stages of pregnancy.142