How do pregnancy tests work?

In ancient Egypt, they had a way to check if a woman was pregnant. They said to pee on wheat and barley seeds and watch them grow. If one of them sprouted, congratulations, you were going to have a baby! If the wheat grew faster, it meant a girl was on the way, and if the barley grew faster, it meant a boy.

A long time later, in 1963, some people did a small test like this and found it could predict pregnancy with about 70% accuracy, but it couldn't say if it was a boy or a girl. They thought it worked because pregnant women's pee had more of a hormone called estrogen, which made the seeds grow. Nowadays, we have much better and faster pregnancy tests.

Modern pregnancy tests all look for a hormone called HCG. This hormone shows up early in pregnancy and tells the body to keep the uterus lining for the baby. As the pregnancy goes on, HCG helps make the placenta, which feeds the baby. The test starts when you put your pee on a special strip. As it moves up the strip, it goes through three important areas.

First, it hits the "reaction zone," where Y-shaped proteins called antibodies grab onto any HCG. These antibodies have an enzyme that can turn on dye later.

Next, the pee carries the enzymes to the "test zone," where the results show up. There are more Y-shaped antibodies here, and if HCG is present, it sticks to them. This kind of test is called a "sandwich assay." If HCG is there, it gets stuck between the antibodies, and the dye-activating enzyme makes a visible pattern.

If there's no HCG, the pee just keeps moving without making a pattern. Finally, there's a "control zone" to make sure the test is working. If there's no pattern in the control zone, it means the test didn't work correctly.

These tests are usually good but not perfect. Sometimes, they might say there's no pregnancy even if it's there because the HCG levels are too low. And if you drink a lot before the test, it can make the pee weaker, so they say to take the test in the morning when your pee is stronger.

On the other hand, sometimes, you can get a false positive (the test says you're pregnant when you're not) because of things like IVF, certain health problems, or cancers. If you want to be sure, it's best to see a doctor. They can use more sensitive tests and measure the exact HCG level in your blood.

Waiting for a pregnancy test result can feel like a long time, but it's all about using science to answer a question and see if your guess was right. And the best part is you don't have to wait until the next harvest like they did in ancient Egypt!

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