The earliest known pregnancy test dates back to 1350 BC in Ancient Egypt.
最早的怀孕检测可以追溯到公元前1350年的古埃及。
According to the Egyptians, all you have to do is urinate on wheat and barley seeds, and wait.
根据埃及人的说法，你只需要在小麦和大麦种子上撒尿，然后等待就可以。
If either sprouts, congratulations, you're pregnant!
如果其中任何一个发芽了，恭喜，你怀孕了！
And if wheat sprouts faster, it's a girl, but if barley, it's a boy.
如果小麦发芽更快些，那就是女孩儿，如果大麦发芽更快些，那就是男孩儿。
In 1963, a small study reproduced this test and found that it predicted pregnancy with a respectable 70% accuracy,
在1963年，一个小研究重新实践了这个实验，发现测孕的准确率高达70%，
though it couldn't reliably tell the sex of the baby.
尽管这个测试无法准确预知孩子的性别。
Scientists hypothesized that the test worked
科学家们认为这个实验能够奏效，
because pregnant women's urine contains more estrogen, which can promote seed growth.
因为怀孕的女性尿液里有更高的雌性激素，它能够使得种子更快发芽。
Now it's easy to take this ancient method for granted
我们很容易觉得这个古老的方法是想当然的，
because modern pregnancy tests give highly accurate results within minutes. So how do they work?
因为现代怀孕测试能够在几分钟内给出高准确度的结果。它是怎么运作的呢？
Over-the-counter pregnancy tests are all designed to detect one thing: a hormone called HCG.
非处方的怀孕检测都是设计来检测出一项指标：一种叫HCG的荷尔蒙。
HCG is produced in the earliest stages of pregnancy
孕早期人体会产生HCG，
and starts a game of telephone that tells the body not to shed the inner lining of the uterus that month.
随后开始了电话游戏，告诉身体当月不要让子宫内膜脱落。
As the pregnancy progresses, HCG supports the formation of the placenta, which transfers nutrients from mother to fetus.
在怀孕的过程中，HCG能够帮助形成胎盘，胎盘能够将母亲体内的营养物质传送给胎儿。
The test starts when urine is applied to the exposed end of the strip.
怀孕测试开始时，尿液覆盖露出来的试纸。
As the fluid travels up the absorbent fibers, it will cross three separate zones, each with an important task.
当尿液流到吸收剂纤维，它将会跨越三个不同的区域，每个区域都有很重要的任务。
When the wave hits the first zone, the reaction zone, Y-shaped proteins called antibodies will grab onto any HCG.
当它到达反应区，Y字形状的蛋白质，也就是抗体，会抓住任何识别到的HCG。
Attached to these antibodies is a handy enzyme with the ability to turn on dye molecules,
附着在这些抗体上的是一种容易取得的酶，这种酶能够激活染料分子，
which will be crucial later down the road.
这种染色分子在后面至关重要。
Then the urine picks up all the AB1 enzymes and carries them to the test zone, which is where the results show up.
然后尿液选择所有AB1酶，把它们带到测试区，最终结果会出现在这里。
Secured to this zone are more Y-shaped antibodies that will also stick to HCG on one of its five binding sites.
这个区域有更多的Y字抗体，在它的五个面都会黏住HCG。

Scientists call this type of test a sandwich assay.
科学家们称这种检测为夹心法。
If HCG is present, it gets sandwiched between the AB1 enzyme and AB2, and sticks to the test zone,
如果有HCG，它会被夹在AB1酶和AB2酶之间，然后黏在测试区，
allowing the attached dye-activating enzyme to do its job and create a visible pattern.
让附带着的染色激活酶发挥作用，创造一个可视的图案。
If there's no HCG, the wave of urine and enzymes just passes on by.
如果没有HCG，尿液和酶就这样流过去了。
Finally, there's one last stop to make, the control zone.
最后，还有最后一站，控制区。
As in any good experiment, this step confirms that the test is working properly.
在每个成功的试验中，这个步骤将会认定前面的测试很好地完成了。
Whether the AB1 enzymes never saw HCG, or they're extras because Zone 1 is overstocked with them,
无论是AB1酶从未发现HCG，还是在第一个反应区里有太多的AB1酶了，
all the unbound AB1 enzymes picked up in Zone 1 should end up here and activate more dye.
所有在反应区里带来的AB1酶都应该在这里结束，刺激更多的染色反应。
So if no pattern appears, that indicates that the test was faulty.
因此，如果没有图案，那就说明这个测试是失败的。
These tests are pretty reliable, but they're not failproof.
这些测试还是值得信赖的，但也有可能失败。
For instance, false negatives can occur if concentrations of HCG aren't high enough for detection.
比如说，如果HCG没有足够多以至能被检测出来，错误的阴性反应就可能会发生。
After implantation, HCG levels double every two to three days, so it may just be too early to tell.
受孕后HCG的水平每两到三天就会倍增，所以也可能是过早而检测不到。
And beverages can dilute the urine sample, which is why doctors recommend taking the test first thing in the morning.
同时，饮料也会冲淡尿液样本，这就是为什么医生建议早上一起床就做这个测试。
On the other hand, false positives can come from other sources of HCG, like IVF injections, ectopic pregnancies,
另一方面，错误的阳性反应也可能来源于其它的HCG，像是试管受精针剂、怀孕异位，
or certain cancers such as uterine cancer or testicular cancer,
或是某种癌症，像是子宫癌或是睾丸癌，
making it possible for one of these tests to tell a man he's pregnant.
这些测试会显示某位男士怀孕了。
The best way for a woman to find out for sure is at the doctor's office.
女士们想要确认怀孕最好的方法是去看医生。
The doctors are also looking for HCG, but with tests that are more sensitive and quantitative,
医生也在寻找HCG，但是医生用的检测会更加敏锐和量化，
which means they can determine the exact level of HCG in your blood.
他们能够判定你血液中HCG的准确水平。
A few minutes can feel like forever when you're waiting on the results of a pregnancy test.
当你等待怀孕测试结果的时候，短短几分钟感觉像是永恒。
But in that brief time, you're witnessing the power of the scientific method.
但在那短暂的时间里，你见证了医学的力量。
That one little stick lets you ask a question, perform a controlled experiment,
那个小小的棒子让你问一个问题，实行一个制式化的实验，
and then analyze the results to check your original hypothesis.
接着分析结果来确认你原先的假设。
And the best part is you won't even have to wait until the next harvest.
最棒的是，你根本不必等到下一次收割。