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The earliest known pregnancy test[br]dates back to 1350 BC in Ancient Egypt.

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According to the Egyptians,

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all you have to do is urinate on wheat [br]and barley seeds, and wait.

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If either sprouts, [br]congratulations, you're pregnant!

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And if wheat sprouts faster, it's a girl,[br]but if barley, it's a boy.

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In 1963, a small study [br]reproduced this test

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and found that it predicted pregnancy[br]with a respectable 70% accuracy,

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though it couldn't reliably [br]tell the sex of the baby.

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Scientists hypothesized [br]that the test worked

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because pregnant women's urine[br]contains more estrogen,

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which can promote seed growth.

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Now it's easy to take [br]this ancient method for granted

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because modern pregnancy tests give[br]highly accurate results within minutes.

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So how do they work?

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Over-the-counter pregnancy tests[br]are all designed to detect one thing:

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a hormone called HCG.

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HCG is produced in [br]the earliest stages of pregnancy

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and starts a game of telephone

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that tells the body not to shed [br]the inner lining of the uterus that month.

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As the pregnancy progresses,

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HCG supports the formation[br]of the placenta,

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which transfers nutrients [br]from mother to fetus.

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The test starts when urine is applied[br]to the exposed end of the strip.

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As the fluid travels up [br]the absorbent fibers,

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it will cross three separate zones,[br]each with an important task.

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When the wave hits the first zone,[br]the reaction zone,

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Y-shaped proteins called antibodies[br]will grab onto any HCG.

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Attached to these antibodies[br]is a handy enzyme

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with the ability to turn on dye molecules,[br]which will be crucial later down the road.

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Then the urine picks up [br]all the AB1 enzymes

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and carries them to the test zone,[br]which is where the results show up.

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Secured to this zone are more[br]Y-shaped antibodies

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that will also stick to HCG[br]on one of its five binding sites.

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Scientists call this type of test[br]a sandwich assay.

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If HCG is present, it gets sandwiched[br]between the AB1 enzyme and AB2,

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and sticks to the test zone,

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allowing the attached dye-activating[br]enzyme to do its job

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and create a visible pattern.

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If there's no HCG, the wave of urine[br]and enzymes just passes on by.

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Finally, there's one last stop to make,[br]the control zone.

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As in any good experiment,

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this step confirms that [br]the test is working properly.

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Whether the AB1 enzymes never saw HCG,

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or they're extras because Zone 1[br]is overstocked with them,

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all the unbound AB1 enzymes picked up[br]in Zone 1 should end up here

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and activate more dye.

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So if no pattern appears,[br]that indicates that the test was faulty.

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These tests are pretty reliable,[br]but they're not failproof.

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For instance, false negatives can occur

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if concentrations of HCG [br]aren't high enough for detection.

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After implantation, HCG levels double[br]every two to three days,

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so it may just be too early to tell.

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And beverages can dilute the urine sample,

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which is why doctors recommend taking[br]the test first thing in the morning.

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On the other hand, false positives[br]can come from other sources of HCG,

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like IVF injections, ectopic pregnancies,

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or certain cancers such as uterine cancer[br]or testicular cancer,

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making it possible for one of these tests[br]to tell a man he's pregnant.

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The best way for a woman to find out [br]for sure is at the doctor's office.

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The doctors are also looking for HCG,

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but with tests that are more sensitive[br]and quantitative,

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which means they can determine[br]the exact level of HCG in your blood.

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A few minutes can feel like forever

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when you're waiting on the results [br]of a pregnancy test.

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But in that brief time, you're witnessing[br]the power of the scientific method.

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That one little stick [br]lets you ask a question,

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perform a controlled experiment,

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and then analyze the results[br]to check your original hypothesis.

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And the best part is you won't even[br]have to wait until the next harvest.