How do pregnancy tests work?
When you take a pregnancy test, it’s looking for the amount of human chorionic gonadotropin (HCG) in your body. You can find HCG in your pee or blood. HCG needs time to build up in your body. Each day of early pregnancy, your body will create more HCG. As the weeks go on, you’ll have more and more HCG in your body, which will make it more likely that a pregnancy test will show as positive. This means if you take a test too soon, it will come back negative.
Pregnancy tests work by reacting to the amount of HCG in either your pee or blood. In a urine test, a piece of reactive paper detects the HCG. This test might show a plus sign, double vertical lines or even the word “pregnant.” Different tests will show a positive result in unique ways. Read the directions that come with the test to know what a positive result will look like. For example, most tests have a control window that shows up first. Seeing a symbol in this window will tell you that the test is working. Keep in mind that different brands of tests will take different amounts of time to show a result.
If you take a blood test, your provider will take a sample of your blood and send it to a lab. The lab will determine the amount of HCG in your blood. Your provider will contact you with your results.
What are the different types of pregnancy tests?
There are two main types of pregnancy tests: urine and blood tests.
Urine tests are typically done at home — though you can have a urine test done at your healthcare provider’s office — while your provider performs a blood test.
At-home pregnancy test
An at-home test uses your pee to look for HCG. They contain special strips that detect HCG. Most at-home pregnancy tests are about 99% effective when used correctly. That’s about the same accuracy rate as pregnancy tests done in your healthcare provider’s office. These tests are available in most drug or grocery stores. They’re easy to use and inexpensive. It’s important to read the instructions on these tests before taking them.
There are three ways to take an at-home pregnancy test:
- Pee in a clean cup. Then, place one to several drops of your pee on a chemical strip.
- Place the pregnancy test strip in your urine stream while you pee.
- Pee in a clean cup and then dip the test strip in the pee while it’s still in the cup.
For many of these tests, HCG can be detected in your urine about 10 days after conception. However, taking it after you miss your period reduces the chance of getting a false-negative result. A missed period typically happens around 14 days after conception.
There are a few things to keep in mind when you take a home pregnancy test, including:
- Use your first morning pee if you can. This is the time of day when your HCG levels will be the most concentrated and easily detected. If you do it at another time of day, try to make sure your pee has been in your bladder for at least three hours.
- Don’t drink excessive amounts of fluids before you take a pregnancy test. This can dilute (thin out) your HCG levels.
- Check the expiration date on the package.
- Read the directions that come with the test thoroughly before starting the test, and follow every step exactly.
Blood test
Another type of pregnancy test is a blood test. Blood tests are rarely done because they’re expensive and tend to have the same result as a urine test. This type of pregnancy test is done using a small sample of blood from a vein in your arm. This blood test not only detects whether the pregnancy hormone is in your body, but can also determine how much of the hormone is present. This is helpful for when your provider needs to know the exact amount of HCG in your blood, not just if there’s HCG in your blood.
A blood test for pregnancy might be done in special circ*mstances, such as for people who are having fertility treatments or when the healthcare provider thinks there might be a problem.
These blood tests are slightly more sensitive than urine tests because they can detect very small levels of HCG. That means they can provide a more accurate answer very early on in pregnancy — within seven to 10 days after conception. For this test, your blood sample is taken at your provider’s office or the hospital, then sent to a lab for analysis. Results might take anywhere from a few hours to two days.
Your provider might also choose to use a blood test to compare HCG levels during the pregnancy. Your HCG levels usually double about every two days during the first few weeks of pregnancy. If the levels don’t rise, it might suggest a problem with the pregnancy. Extremely high HCG levels might mean that you’re carrying twins or that there’s an issue with the pregnancy.
Are all home pregnancy testing methods the same?
Most brands of at-home pregnancy tests are reliable. Although the exact testing method of different pregnancy tests can differ from one type to the other, they all look for HCG in your body. If you’re using an at-home test, most will give you the same result. The difference with your at-home tests will be the sensitivity of the test. Some might be more sensitive than others and produce a positive result (detect HCG in your urine) sooner than others. For the most accurate reading, it’s still recommended that you wait until you’ve missed your period. At that point, all tests should be accurate.
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What are the advantages of using a home pregnancy test?
There are quite a few advantages to using a home pregnancy test, including:
- Pregnancy tests are inexpensive.
- They’re easy to use.
- Home tests provide results quickly.
According to pregnancy kit manufacturers, most at-home pregnancy tests are 98% to 99% accurate when you use them exactly as instructed. Positive results can be trusted, but you can get a false negative result if you take the test too soon.
Blood tests tend to be more expensive and inconvenient. However, blood tests can detect pregnancy sooner and are the only tests to show specific amounts of HCG in your body.
Is there anything you shouldn’t do before a pregnancy test?
Most pregnancy tests don’t ask you to avoid activities or change your lifestyle. The only medication that may interfere with your results is fertility medication containing HCG.
Here are some helpful tips you should follow for the best results:
- Read the instructions carefully before doing anything.
- Wait until you miss your period to take the test.
- Use your first pee or pee from a full bladder. Chugging water before your test in order to pee may affect your results.
