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How does implantation in the uterine lining prevent menstruation?

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Front view anatomical diagrams of the male and female reproductive systems, with labeled organs including penis, testis, prostate gland, uterus, ovary, and vagina. — human reproductive system Organs and structures of the male and female reproductive systems.

When a fertilized ovum undergoes implantation into the endometrium, it prevents menstruation by altering the hormonal signals that otherwise trigger the shedding of the uterine lining.12

Normally, if fertilization does not occur, the corpus luteum in the ovary has a limited lifespan of about 14 days, after which it degenerates, leading to a drop in progesterone levels and the onset of menstruation.23

However, upon successful implantation, cells of the blastocyst begin producing hormones, most notably human chorionic gonadotropin (HCG). This hormone acts to prolong the life and activity of the corpus luteum. By maintaining the corpus luteum, the body ensures a continued supply of progesterone, which prevents the breakdown of the endometrium and instead stimulates its further thickening to support the developing pregnancy.2413