Pregnancy tests, consisting of an immunoassay strip, rely on the presence of the hormone human chorionic gonadotropin (hCG), a glycoprotein that is secreted by the placenta shortly after fertilization. 

 

The tests work by binding the hCG hormone, from either blood or urine, to an antibody and an indicator. The antibody will only bind to hCG; other hormones will not give a positive test result. The usual indicator is a pigment molecule, present in a line across a home pregnancy urine test. Highly sensitive tests could use a fluorescent or radioactive molecule attached to the antibody.

 

Pregnancy test could be traced back to as far as 1350 BCE, when the Egyptians had women urinate on barley and wheat to test pregnancy. Testing it in the 1900s, this provides a moderate rate of success as some of the plants do grow. This is the first test to detect a unique substance in the urine of pregnant women that promotes the growth of the plants.  

 

During the Middle Ages, again women’s urine was used only this time its colour was examined. Pregnant women’s urine was said to be  “clear pale lemon color leaning toward off-white, having a cloud on its surface.” Other tests also include mixing wine with urine. It has been found that alcohol reacts with certain proteins in urine, so this wouldn’t have been reliable. 

 

By 1890, scientists have speculate that the human organs excrete substance Ernest Starling calls “hormones”. It wasn’t until the 1920 that it was found a specific hormone (later known as hCG) that only pregnant women excrete.