hCG

Human chorionic gonadotropin (hCG) is a glycoprotein hormone produced mainly by placental trophoblast cells after implantation. It consists of two subunits, alpha and beta; the alpha subunit is shared with LH, FSH, and TSH, while the beta subunit is unique to hCG and confers biological specificity.

Because of its LH-like activity, hCG supports the corpus luteum in early pregnancy, maintaining progesterone production until the placenta takes over around the end of the first trimester. The hormone also stimulates testosterone production in men when used therapeutically.

Diagnosis and testing: hCG is the target of pregnancy tests; it can be detected in blood or urine within about 1–2 weeks after conception.

Clinical uses: In assisted reproduction, synthetic or natural hCG is used to trigger final oocyte maturation and ovulation in combination with follicle-stimulating hormone. In men with hypogonadotropic hypogonadism, hCG stimulates Leydig cells to produce testosterone and, with FSH, can promote spermatogenesis. hCG is also used in some treatments following gonadotoxic therapy or to treat certain infertility disorders.

Production and forms: Naturally produced by the placenta; recombinant hCG is manufactured for medical use. hCG assays are used in pregnancy testing; quantitative hCG levels help monitor early pregnancy and ectopic risk.

Safety and adverse effects: Potential adverse effects include edema, abdominal pain, fatigue, and ovarian hyperstimulation syndrome in women undergoing fertility treatment; there is a risk of multiple pregnancy. Elevated hCG levels can indicate gestational trophoblastic disease or certain cancers; as such, abnormal hCG can be a tumor marker.