Pregnancy (hCG)

Pregnancy testing and hCG

Evidence for testing to detect pregnancy has been found as far back as ancient Egyptian cultures. In the early twentieth century human chorionic gonadotropin (hCG) was identified as the major hormone associated with pregnancy.  The first pregnancy test based on hCG was called the ‘Rabbit test’ and were based on a bioassay in which urine was injected into young female rabbits. If hCG was present the rabbit ovaries would be enlarged.  Immunoassays for hCG were developed around 1960 and were latex agglutination assays. More recently enzyme-linked immunoassays were developed. The most commonly used pregnancy tests either in doctor's offices or over-the-counter (OTC) tests are based on lateral flow tests.

Human chorionic gonadotropin (hCG)

hCG is a small glycoprotein hormone produced by cells that form the placenta. It stimulates progesterone production by the ovary and the placenta and helps maintain the pregnancy. hCG is composed of two different subunits, alpha (α) and beta (β). The alpha subunit is common to all members of the glycoprotein-hormone family and the beta subunit is unique to hCG and confers its biological activity. All pregnancy tests are based on the beta subunit. There are many different forms of hCG based on the degree of glycosylation and different proteolytic forms. Not all hCG tests detect or measure all these forms of hCG equally. Although measurement o hCG is primarily done to detect pregnancy, hCG is used for other purposes such as detecting certain types of cancer.