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How do pregnancy tests work? - Tien Nguyen


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Over-the-counter pregnancy tests give potentially life-changing results with a pretty high rate of accuracy. But how do they work? Tien Nguyen explains how each test performs a scientifically rigorous, multi-stage experiment that goes from start to finish in the time that it’ll take you to watch this video.

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Pregnancy tests have been commercially available since the 1970s, and they’ve evolved since then. The first over the counter test, made by e.p.t., came as a whole kit that included test tubes, funnels and various solutions, and took about 2 hours to administer! Many things have changed since then.

The National Institutes of Health provides a timeline for the development of pregnancy tests. Visit the site and follow the timeline of pregnancy testing.

In the 1990s, technology that took advantage of antibodies was developed. Antibodies are large proteins produced by the immune system that can bind to particular regions called epitopes on antigens. Antigens can be any foreign substance. Antibodies consist of amino acids and have a Y-shape. The top part of an antibody’s Y-shape binds to the epitope on the antigen, while the bottom (stick) part of the Y is mostly the same between different antibodies. Here’s a video that explains the structure of antibodies by Armando Hasudungan.

Different tests use different dye/dye-activating enzymes to indicate the test results. But generally speaking, the dye-activating enzyme chemically reacts with the dye molecules to form a new product that is a colored. Pregnancy tests done in doctors’ offices are blood tests. They are quite sensitive and can detect levels of hCG down to 2-5 IU/mL, while the best over-the-counter tests detect ~25 mIU/mL. Read a little more about how pregnancy tests work here.

Then, for a more detailed and interactive graphic on how pregnancy tests work, visit this site.

Interested in the Egyptian pregnancy seed test? It was replicated in 1963. Read the article here.

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TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Tien Nguyen
  • Director Andrew Foerster
  • Artist Mike Ellis
  • Narrator Susan Zimmerman

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