Pregnancy Tests: How They Work, Types & Accuracy

What is a pregnancy test, and how does it work?

A pregnancy test can tell you whether you are pregnant. You can do an at-home pregnancy test in the privacy of your own home, or visit your doctor to do an in-office pregnancy test. According to the Department of Health and Human Services (DHHS), a home pregnancy test provides a 99 percent accuracy rate, as long as you use the test correctly.

A pregnancy test works by detecting a hormone called human chorionic gonadotropin (hCG) in your blood or urine. Also known as the pregnancy hormone, hCG is produced by your body after a fertilized egg has been implanted in your uterus, which usually occurs about 10 days after conception. HCG is only present in your body when you are pregnant, reports the DHHS. Therefore, if the pregnancy test detects this hormone in your blood or urine, your results will display as positive.

According to DHHS, HCG builds up in your system relatively quickly when you are pregnant. However, if you take a pregnancy test too soon after conception, it’s possible your hCG levels may not be high enough to produce a positive pregnancy test. If your pregnancy test results come back negative but you still think you may be pregnant, wait a few extra days and take another test to confirm your pregnancy status.

What types of pregnancy tests are available?

There are two types of pregnancy tests: a urine test and a blood test.

Most home pregnancy tests are urine tests, which are non-invasive and require you to urinate on a stick, or into a cup into which a stick can be dipped to detect hCG. A blood test can only be performed at your doctor’s office or a lab. According to the DHHS, a blood test can detect pregnancy earlier than most urine tests but takes longer than a urine test to produce results.

Home pregnancy tests are relatively easy to use and come with a brief set of instructions telling you how to use the test and get accurate results. The DHHS says most tests require you to urinate directly on a stick, then wait up to two minutes for the test to detect hCG in your urine. Within two minutes, a symbol or the words “pregnant” or “not pregnant” will show up on the test to reveal whether you are pregnant.

How accurate are pregnancy tests?

According to DHHS, pregnancy tests are 99 percent accurate, as they work by detecting the hCG hormone that is only present in your body when you are pregnant. If you are not pregnant, your body does not make hCG, and it will not show up in pregnancy test results.

Some factors, according to DHHS, including expiration date and how and when you use it may affect the accuracy of your pregnancy test. Using a test well after its expiration date may result in a false negative or false positive. Using it too early within a few days of conception may result in a false negative, especially if your body isn’t making enough hCG for the test to detect.

When to take a pregnancy test

The DHHS recommends waiting until after your first missed period to take a pregnancy test, and to wait 10 minutes for results to show up on the test. Some pregnancy test brands may detect hCG in your urine earlier than others, though waiting until after your first missed period may produce the most accurate results. Your doctor can also give you sound advice regarding when to take a pregnancy test.

Where can I get a home pregnancy test?

Home pregnancy tests are widely available and can be purchased at nearly any drugstore, pharmacy, or grocery store. Before buying a home pregnancy test, check its expiration date to make sure it’s still current and to avoid inaccurate results.

What do the pregnancy test results mean?

Results on a pregnancy test are usually easy to read and interpret. Most tests will display a positive sign or the word “pregnant” if you are pregnant, or a line, a negative symbol, or the words “not pregnant” if you are not pregnant. The DHHS recommends reading the instructions on your pregnancy test to determine how to interpret your results.

If your results are positive, the National Institutes of Health (NIH) recommends making an appointment with your healthcare provider as soon as possible. Your doctor or midwife can perform an evaluation and work with you throughout your pregnancy to help ensure you and your baby stay healthy.