Human chorionic gonadotropin

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Human chorionic gonadotropin (hCG) is a peptide hormone produced in pregnancy, that is made by the embryo soon after conception. Its primary role is to cause progesterone secretion by the corpus luteum, thereby readying the uterine lining for implantation by the fertilized egg.

Table of contents

1 Structure
2 Function
3 Pregnancy testing

Structure

hCG is a glycoprotein composed of 237 amino acids with a molecular mass of 36.7 kDa [1]. It is heterodimeric, with an α (alpha) subunit identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). Its β (beta) subunit is unique to hCG.

Function

hCG promotes the maintenance of the corpus luteum and causes it to secrete the hormone progesterone. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus.

Because of its similarity to LH and FSH, hCG can also be used clinically to induce ovulation in the ovaries as well as testosterone production in the testes.

Pregnancy testing

Pregnancy tests measure the levels of hCG in the blood or urine to indicate the presence or absence of a fertilized egg. In particular, most pregnancy tests employ an antibody that is specific to the beta subunit of hCG. This is important so that tests do not make false positives by confusing hCG with LH and FSH. (The latter two are always present in the body, while hCG levels are negligible except during pregnancy.)