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View full lesson: http://ed.ted.com/lessons/how-do-pregnancy-tests-work-tien-nguyen 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. Lesson by Tien Nguyen, animation by Andrew Foerster.