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How does human chorionic gonadotropin support early pregnancy?

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Diagram comparing reproductive pathways: arrows show sexual reproduction forming a diploid zygote from oocyte and sperm, haploid parthenogenesis forming a haploid individual, and two types of diploid parthenogenesis-automixis and apomixis-both resulting in diploid individuals. Symbols indicate haploid and diploid stages. — Animal reproductive system The process of sexual reproduction and several forms of parthenogenesis.

Human chorionic gonadotropin (HCG) is a glycoprotein hormone secreted by the placenta (specifically the chorionic layers) following the implantation of a fertilized egg.12

Its primary role in supporting early pregnancy is to maintain the function of the corpus luteum. Under normal conditions, the corpus luteum has a limited lifespan and will degenerate if fertilization does not occur, leading to menstruation. However, HCG acts to prolong the life of the corpus luteum, keeping it in an active state for at least the first two months of pregnancy.134

By maintaining the corpus luteum, HCG ensures the continued production of [progesterone]. Progesterone is essential for pregnancy because it prepares the uterus for the developing embryo by increasing blood supply and inhibiting muscular contractions that might otherwise reject the implanted egg. The corpus luteum continues this vital hormone-producing function until the placental tissue is sufficiently developed to take over.345