What prevents the uterine lining from being shed if an egg is fertilized?

If an egg is fertilized, the developing embryo produces human chorionic gonadotropin (hCG), a hormone that signals the body to maintain the uterine lining. hCG stimulates the corpus luteum to continue producing progesterone, which thickens and sustains the uterine lining, preventing it from being shed. This hormonal support is crucial for creating a suitable environment for the embryo to implant and grow.