False Positive Pregnancy Test: Can it Happen to You?

Home pregnancy tests work by checking for the presence of human chorionic gonadotropin, or hCG, in your body. Known as the pregnancy hormone, the manifestation of hCG in your body typically means a beautiful new baby is on the way. While most hCG pregnancy tests are accurate 99 percent of the time, some false positive tests do occur.

What is a False Positive Pregnancy Test?

As its name suggests, a false positive pregnancy test occurs when the test reads positive but you’re NOT actually pregnant. A false negative pregnancy test, on the other hand, means you ARE in fact pregnant even though the test reads negative.

How False Positive Pregnancy Results Occur

A pregnancy test result that is truly false positive due to a malfunctioning home pregnancy test kit is a rare occurrence. Therefore, if you have a single positive pregnancy test result and subsequent tests have been negative, it’s generally due to one of the following reasons:

Chemical Pregnancy

While terribly unfortunate, nearly 25 percent of all pregnancies result in a chemical pregnancy. This happens when a woman becomes pregnant, receives a positive pregnancy test result, and miscarries shortly afterwards. Since home pregnancy tests continue to advance and allow women to detect pregnancy earlier and earlier, more instances of chemical pregnancy are occurring. While a chemical pregnancy isn’t necessarily a false positive pregnancy reading, it’s a very real possibility and you should see a healthcare professional for confirmation and to ensure a healthy pregnancy.

Missed Reaction Time

It’s important to follow the instructions to a tee when taking a home pregnancy test in order to get the most accurate reading possible. All tests clearly state on the box or in the instructions how long the test should sit prior to reading the results. If you wait too long, you should consider any results to be invalid. Interpreting the results after the recommended timeframe can result in false positive readings.

Fertility Treatments

If you’re trying to conceive with the help of fertility treatments, for example having hCG or gonadotropin fertility shots such as Pergonal, Pregynl, APL, or Profassi to increase ovulation, you may experience a false positive pregnancy reading for up to three weeks after receiving the shot. Since the hCG shot needs time to metabolize and exit your system, fertility doctors recommend waiting at least two weeks before taking a pregnancy test.

Evaporation Lines

An evaporation line can appear on some pregnancy tests. This happens when the urine gets into the results area. Although the faint, grayish color of the evaporation line isn’t the same color as the line depicted in the test instructions as representing a positive result, some women interpret the presence of the line as a positive reading.

Improper Testing Times

Most women trying to conceive want to find out whether or not they’re pregnant as soon as possible. However, in order to get an accurate reading when taking a home pregnancy test, it’s best to wait two weeks after not receiving your scheduled period. By waiting two weeks, your hCG levels will be high enough to be detected by the test and render a positive result. While there are many home pregnancy tests claiming to be able to detect pregnancy up to five days prior to your period being due, these tests are usually only accurate 97 percent of the time when following the instructions exactly. Therefore, it’s usually best to stick to the two-week rule.

Medical Conditions

Ovarian cysts, menopause, ectopic pregnancy and other types of medical conditions can also lead to misleading results. One such medical condition, which is very rare with only 3,000 cases taking place in the US each year, is the existence of a trophoblastic tumor. A trophoblastic tumor forms when an egg isn’t properly fertilized, resulting in the growth of a tumor instead of a baby. These tumors produce hCG, hence their ability to produce false positive pregnancy test results.

Avoiding a False Positive Test Result

As you can see, there are plenty of reasons for the occurrence of a false positive pregnancy test result. Although false positive results due to defective tests are very rare, there are a variety of factors from hCG fertility shots to improper testing times that can affect the results of the test. There’s nothing you can really do to avoid a false positive test result other than adhering to the two-week rule and the test instructions, but the majority of experts recommend taking a second pregnancy test as a preliminary confirmation of a positive result. If the second test comes back positive as well, you should contact your doctor to officially confirm your pregnancy.