How Accurate Are Pregnancy Tests?

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Manufacturers claim pregnancy tests are between 97 percent and 99 percent accurate. Accuracy is highly dependent on the brand and when the test is taken.

Though most pregnancy tests work in the same way, some are more sensitive than others. That's why the brand of pregnancy test being used plays a role in how accurate the result is. However, the factor that has the biggest impact on the accuracy of the test is if it is used correctly. Women should be sure to read the instructions thoroughly before administering the test to ensure the best results.

How Pregnancy Tests Work
Home pregnancy tests work by recording the presence of human chorionic gonadotropin (hCG) in the urine. This hormone is typically not present in a woman's system unless she is pregnant. Most tests require women take the test first thing in the morning when their bladder is full. Women should avoid drinking large amounts of water before taking the test, notes Parents magazine. Doing so dilutes the urine making the level of hCG too low to be detected by the test. As a result, the test could reveal a false negative.

When to Take a Pregnancy Test
How far along a woman is into her pregnancy also plays a role in the accuracy of the test result. The excitement of trying to conceive makes it difficult for some women to wait several weeks to take the test, but this is necessary for an accurate result. Some brands are more sensitive than others and boast an accurate reading up to six days before a missed period. However, most brands recommend women wait until after missing a period to take the test. This allows hCG to reach a detectable level. Taking the test too soon could result in a false negative.

Factors That Affect the Accuracy of a Pregnancy Test
In addition to the factors listed above, checking the results too soon and certain medications can also affect the result of a home pregnancy test. Women need to wait several minutes after taking the test before reading the results. This gives the test time to detect hCG and show a result. It will appear negative or won't have a reading at all until the appropriate amount of time has elapsed. Pregnancy tests with digital displays are designed to be easier to read because they clearly display "Pregnant" or "Not Pregnant" when the test is ready. Most medications have no effect on the results of a pregnancy test; however, women taking fertility medications that contain hCG might receive inaccurate results on a home pregnancy test.

When taken correctly, home pregnancy tests are up to 99 percent accurate. Getting a false positive is rare, but false negative responses are quite common. Taking the test exactly as directly reduces the chances of getting a false positive reading. A positive result indicates a pregnancy; however, it could also indicate an ectopic pregnancy, menopause or problems with the ovaries, states the Mayo Clinic. For this reason, women should schedule an appointment with their health care provider if they get a positive result on their pregnancy test.