Home Pregnancy Tests

The U.S. military was prepared if the Cold War turn hot. It had contracts for such emergency provisions as ammunition and rations. And agreements to supply giant chinchilla rabbits. 

No, the rabbits were not some kind of secret biological weapon. Instead, they were used for state-of-the-art early pregnancy tests. Doctors would inject the rabbit with a woman's urine. If it contained hCG, a hormone found in pregnancy, the rabbit's ovaries turned bright yellow. 

This is very different from today's home pregnancy tests. Just dip the tip of the thermometer-shaped plastic device in urine for a few seconds. If hCG is present, a blue line appears within minutes. 

It took biomedical engineers decades to create something this simple. Their first challenge was to "see" the miniscule amounts of hCG in urine. To put the problem into perspective, it was like measuring six ten-thousandths of an ounce of hCG mixed into a 660,000-gallon Olympic-sized swimming pool. 

By the 1960s, companies had developed tests that measured hCG in urine samples, usually by adding a chemical that caused them to clump together. The first home pregnancy test was released in 1977, tried to simplify the laboratory process. It took two hours to complete its nine steps. It used color instead of clumping to indicate pregnancy.

By the mid-1980s, simpler systems appeared that were much faster. The key was the use of absorbent paper pads loaded with color-tagged antibodies. The antibodies latched onto hCG molecules as they passed by. As these bonded molecules moved along the paper, they reached a group of other antibodies arrayed in a line across the paper. If woman had hCG in her urine, this line of antibodies would stop the molecules from moving. When enough of them accumulated, their color tags formed a visible blue line, indicating pregnancy. 

The tests were fast and accurate. What is more, the use of antibody-loaded paper technology was adapted for all types of diagnostics, including medical (such as the Covid-19 test), veterinary, and environmental testing.