WEBVTT

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The earliest known pregnancy test
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 
and barley seeds, and wait.

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If either sprouts, 
congratulations, you're pregnant!

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

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In 1963, a small study 
reproduced this test

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

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

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Scientists hypothesized 
that the test worked

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because pregnant women's urine
contains more estrogen,

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which can promote seed growth.

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

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because modern pregnancy tests give
highly accurate results within minutes.

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So how do they work?

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

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a hormone called HCG.

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HCG is produced in 
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 
the inner lining of the uterus that month.

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As the pregnancy progresses,

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HCG supports the formation
of the placenta,

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which transfers nutrients 
from mother to fetus.

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

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As the fluid travels up 
the absorbent fibers,

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

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When the wave hits the first zone,
the reaction zone,

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

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Attached to these antibodies
is a handy enzyme

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

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Then the urine picks up 
all the AB1 enzymes

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

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Secured to this zone are more
Y-shaped antibodies

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

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Scientists call this type of test
a sandwich assay.

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If HCG is present, it gets sandwiched
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
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
and enzymes just passes on by.

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

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As in any good experiment,

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this step confirms that 
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
is overstocked with them,

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

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and activate more dye.

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

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

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For instance, false negatives can occur

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

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After implantation, HCG levels double
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
the test first thing in the morning.

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

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like IBF injections, ectopic pregnancies,

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or certain cancers such as uterine cancer
or testicular cancer,

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

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

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The doctor's are also looking for HCG,

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but with tests that are more sensitive
and quantitative,

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which means they can determine
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 
of a pregnancy test.

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

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That one little stick 
lets you ask a question,

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perform a controlled experiment,

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and then analyze the results
to check your original hypothesis.

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