Pregnancy Test

How Does a Pregnancy Test Work?

Whether you are dying to have a baby, or whether it is the last thing on your mind, chances are, at some time in your life, you have wondered how pregnancy tests work.

In this article, we look at how they work, how accurate they are, and what, if anything, can affect the results.

What Do Pregnancy Tests Do?

Pregnancy tests work by picking up elevated levels of hCG, the human growth hormone in the urine.  This hormone is usually only secreted in levels that the test is capable of discerning from around six days after conception occurs, and that is why you are usually told to wait until your period is late before trying them.

The tests use an antibody and an indicator, and without going too much into the science of it, they both bind to the hormone.  That is what makes the line show up in the window when you take the test.

Are Home Pregnancy Tests Accurate?

Yes. If used correctly, a home pregnancy test is almost as accurate as those used by your doctor are. That is, unless your doctor performs a blood test. There are some tests that are more accurate, but if you use most over the counter tests properly, there is about a 99% chance the result is accurate.

Is There Anything That Affects a Pregnancy Test?

Many people worry about false positives and negatives. The best way to rule out a false negative is to make sure that you wait until your period is late, and to use your first morning urine, which has the highest concentration of hCG.

Sometimes, what is seen as a positive on a test is in fact a pregnancy, but the pregnancy does not ‘take’ and the embryo is lost.

There are also very few drugs that will affect the result of a pregnancy test – with the exception of fertility drugs, which often increase hCG levels to a degree where they can show a false positive.

Finally, sometimes, the evaporation of your urine will result in a second line on the test, which would appear to be positive, but is in fact not. That is why most tests offer a time limit in which the test can be accurately read.


  1. Pregnancy tests use the level of hCG in your body to determine pregnancy.
  2. Over the counter tests are usually between 97 and 99 percent accurate.
  3. Urine tests should only be taken when you miss a period, to ensure that it is accurate.
  4. Used correctly, a home pregnancy kit is almost as accurate as a test your doctor will perform.

Include Your Review Below

Previous post:

Next post: