False Positive Pregnancy Test: 4 Reasons & How to Prevent

A pregnancy test can show a false positive. Although this is a rare occurrence, this most frequently happens with home pregnancy tests due to errors when using it or due to expiry.

Another common cause for a false positive is a chemical pregnancy. This occurs when the egg has been fertilized, but is unable to properly implant on the uterine lining. It is unable to develop into a full fetus, but the body initiates the production of hormones anyway, giving the test a positive result. A pregnancy that does not continue however will eventually show a negative pregnancy result. 

In addition, many women who undergo fertility treatments with hCG injections will often see false positives, as well as women who unknowingly have tumors that produce hCG. 

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Main causes of false positive tests 

Changes in test results generally occur when the test has expired, and therefore it is very important to confirm the expiry test before using it. If the expiry date is correct, other reasons for a false positive may include: 

1. Test done incorrectly

Before using a home pregnancy test, be sure to read the package instructions. Pay attention to the time necessary to read the result, as some test results may change after a set time. 

In addition, before using the test, you should cleanse the genital area with water, as some soaps or creams can impact the test results, and show a false positive or false negative. 

Learn more about how to take a home pregnancy test

2. Chemical pregnancy 

This type of pregnancy occurs when the egg is fertilized, but the embryo is unable to implant into the uterus. In these cases, the body will start to produce hCG hormone, and therefore it will be detected in the urine or the blood. However, because the embryo fails to implant, it will eventually lead to a miscarriage, which can be confused for a late period. 

3. Use of some medications

Some medications used for fertility treatments contain high quantities of hCG. This hormone is what is identified in pregnancy tests, which can lead to false positive soon after a treatment. 

Other more common medications, like anticonvulsants, diuretics or tranquilizers can also cause changes to the final result. Therefore, it is important to read your medication pamphlets before completing a home pregnancy test, or to complete a blood test in the lab for more accurate results.

4. Health problems  

Although this is more rare, a false positive can also occur with some illnesses. This can happen, for example, with tumors that produce hormones, like breast cancer or ovarian cancer. 

Read about causes of false negative pregnancy tests

How to prevent a false positive 

To prevent a false positive result, it is important to follow the instructions as outlined in the pregnancy test package. After the test, you should also: 

  • Repeat the test 3 to 5 days later 
  • Do not reference your results after the indicated time 
  • Book an appointment with your doctor within the next month 

The best way to prevent changes to your result is to complete an hCG blood test, as there is less room for error with this test method. Read more about the advantages and disadvantages of different pregnancy tests. In addition, before the test, the doctor will be able to evaluate whether there are any medications or health circumstances that can alter the results.