A hormone produced by an implanting embryo. If this hormone is present in a woman’s blood, it indicates a possible pregnancy. It can also be given to women undergoing fertility treatment to trigger ovulation, for example, if she is undergoing IVF. hCG injections may also be given post-embryo transfer to encourage progesterone production and promote implantation. Fun fact: the hormone hCG that’s taken as a drug is actually extracted from the urine of pregnant women.