Human chorionic gonadotrophin; hCG; Novarel; Ovidrel; Pregnyl; A.P.L; Profasi; Chorex; Chorigon; Chorigon-10
Human chorionic gonadotrophin is a hormone produced by the cells that surround the growing human embryo; these cells will eventually go on to form the placenta. Human chorionic gonadotrophin can be detected in the urine from 7-9 days post-fertilisation as the embryo attaches and implants in the womb; it forms the basis of most over-the-counter and hospital pregnancy tests (see photo).
During the menstrual cycle, when an egg is released from the ovary at ovulation, the remnants of the ovarian follicle (which enclosed the egg) form a new, temporary ovarian gland called the corpus luteum, which produces the hormone progesterone. If, after two weeks, the ovulated egg remains unfertilised, the corpus luteum stops producing progesterone, and breaks down. Through a feedback mechanism, this signals the pituitary gland to produce follicle stimulating hormone (and to a lesser extent luteinising hormone) to initiate the next menstrual cycle. However, in the event that the ovulated egg is fertilised by sperm and an embryo is conceived, it is vital that the corpus luteum continues to produce progesterone until the placenta is established (the placenta then takes over progesterone production). It is important that the corpus luteum keeps producing progesterone because loss of progesterone leads to shedding of the womb lining (menstruation), which would prevent an embryo from implanting. Human chorionic gonadotrophin is the embryonic hormone that ensures the corpus luteum continues to produce progesterone throughout the first trimester of pregnancy.
As well as maintaining progesterone production from the ovary, human chorionic gonadotrophin may also play a role in making sure the lining of the uterus (endometrium) is ready to receive the implanting embryo. Recent studies have indicated that human chorionic gonadotrophin may help to increase the blood supply to the uterus and be involved in re-shaping the lining of the uterus in preparation for the implanting embryo.
Human chorionic gonadotrophin is produced by the trophoblast cells which surround the developing embryo at approximately day five of pregnancy. The amount of human chorionic gonadotrophin in the bloodstream doubles every 2-3 days as development of the embryo and placenta continue, and levels peak at around six weeks of pregnancy. Following this peak, levels of human chorionic gonadotrophin fall (although they remain detectable throughout pregnancy). Once the placenta is established, it becomes the main source of progesterone production (around week 12 of pregnancy), and human chorionic gonadotrophin is no longer required to maintain ovarian function. However, human chorionic gonadotrophin may have additional beneficial effects in the latter stages of pregnancy; such roles are currently being investigated by researchers.
There is no strong evidence that high levels of human chorionic gonadotrophin cause direct negative consequences. Very high levels of human chorionic gonadotrophin are rare but can indicate hyper-proliferation of the placenta (also referred to as hydatidiform moles or molar pregnancies), which can lead to cancer (choriocarcinomas) in some cases. Levels of human chorionic gonadotrophin may also be elevated sometimes in association with some non-pregnancy related cancers (e.g. kidney, breast, lung and gastrointestinal tract). In such cases, levels of human chorionic gonadotrophin in the blood/urine can serve as a tumour marker.
In pregnancy, a link between high levels of human chorionic gonadotrophin and occurrence of Down’s syndrome has also been suggested. Studies have shown that the levels of human chorionic gonadotrophin in a Down’s syndrome pregnancy are approximately twice that of an unaffected pregnancy. However, high levels of human chorionic gonadotrophin do not cause Down’s syndrome (rather it is caused by an extra chromosome at position 21); further research is needed to investigate this link.
Low levels of human chorionic gonadotrophin can indicate a failing pregnancy. Reduced levels of human chorionic gonadotrophin are often observed in ectopic pregnancies (where the embryo implants outside of the uterus) or in miscarriages.
Last reviewed: Mar 2018