Human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a glycoprotein hormone produced mainly by placental trophoblast cells during pregnancy. It maintains progesterone production early in pregnancy and is the hormone detected by pregnancy tests.

Syncytiotrophoblast: The multinucleated outer layer of placental trophoblast that contacts maternal blood and secretes hormones. This placental cell layer is the principal source of hCG entering maternal circulation.
Glycoprotein hormone: A hormone consisting of a protein component covalently modified with carbohydrate chains. hCG belongs to this hormone class and carries carbohydrate chains that affect its circulation.
Quantitative hCG test: A blood assay that measures the concentration of human chorionic gonadotropin. Serial measurements help assess early pregnancy and investigate abnormal pregnancy patterns.
Follicle-stimulating hormone: A pituitary glycoprotein hormone that promotes ovarian follicle development and sperm production. It shares the glycoprotein hormone architecture but does not sustain the corpus luteum like hCG.
Luteinizing hormone/choriogonadotropin receptor: A cell-surface receptor activated by luteinizing hormone and human chorionic gonadotropin. hCG binds this receptor on the corpus luteum to sustain progesterone secretion.
Glycosylation: The enzymatic attachment of carbohydrate groups to proteins or lipids. hCG’s carbohydrate modifications influence its stability and biological activity.
Ectopic pregnancy: A pregnancy implanted outside the uterine cavity, most often in a fallopian tube. hCG trends can support evaluation, though they cannot alone locate a pregnancy.
Thyroid-stimulating hormone: A pituitary glycoprotein hormone that stimulates thyroid hormone production. It shares an alpha subunit with hCG but acts at a different receptor and organ.
Corpus luteum: A temporary ovarian endocrine structure formed from a follicle after ovulation. It responds to hCG by continuing progesterone production in early pregnancy.
Alpha subunit: The common protein subunit shared by several glycoprotein hormones, including hCG, LH, FSH, and TSH. hCG pairs this shared subunit with its distinctive beta subunit.

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