At-home medical diagnosis dates back to the early 18th century and the invention of the enclosed thermometer. Since then, human ingenuity has devised ways to detect an assortment of medical conditions. The market for such devices has flourished since 1977, when the Food and Drug Administration approved the home pregnancy test.

The pregnancy test checks a woman¿s urine for human chorionic gonadotropin (hCG), a hormone produced by the placenta after egg fertilization. Its concentration in the blood doubles every two to three days, peaking around the eighth week of pregnancy.The technology for the test depends on antibodies--Y-shaped proteins that our immune system normally deploys against invading viruses, bacteria or anything else alien to the body.

This article was originally published with the title Pregnancy Tests.

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