A pregnancy test can sometimes show a false positive result, which means it detects the pregnancy hormone hCG even when the person taking the test is not actually pregnant. False positive pregnancy tests are quite rare in comparison to false negative tests, which fail to detect pregnancy when the person is indeed pregnant. However, false positives can still happen and may leave someone thinking they are expecting when they are not. Understanding the potential causes of false positive pregnancy tests can help explain this confusing situation.
What is a false positive pregnancy test?
A false positive pregnancy test occurs when the test indicates that the woman is pregnant, but she actually is not pregnant. This happens when the pregnancy test incorrectly detects the presence of the pregnancy hormone human chorionic gonadotropin (hCG) in a non-pregnant woman’s urine or blood.
A false positive test result will show two lines (a colored line next to the “Test” wording and a colored line next to the “Control” wording). This is interpreted as a positive result for pregnancy when in reality the woman is not pregnant.
How accurate are pregnancy tests?
Home pregnancy tests available today are very accurate when used properly, with false positives being quite uncommon. Modern home pregnancy tests measure levels of the hCG hormone, which begins to rise soon after implantation of a fertilized egg. The claimed accuracy of home pregnancy tests exceeds 99% when used according to instructions.
False positives are more likely to occur with expired tests or if testing is done too early before enough hCG hormone has accumulated to be detectable. Using a test properly as directed and confirming any positive result with a repeat test reduces chances of recording a false positive.
Causes of false positive pregnancy tests
While very rare, there are a few reasons why a pregnancy test may detect the hCG hormone and show positive even when the woman is not pregnant:
Testing too soon after taking fertility medications
Medications containing hCG may cause false positive pregnancy tests for days or weeks after the last dose was taken. Fertility drugs containing hCG include Pregnyl and Novarel. The pregnancy test may pick up leftovers of the hCG shot used to trigger ovulation or help with egg maturation.
Prior pregnancy
The pregnancy hormone hCG may remain in the body for up to 12 weeks after a pregnancy ends. This means leftover hCG can make pregnancy tests positive after experiencing a miscarriage or having an abortion.
Ectopic pregnancy
A pregnancy test may be positive if conception occurred but the fertilized egg implanted outside the uterus in a fallopian tube or ovary rather than inside the uterus. This is called an ectopic pregnancy which is not viable but still produces hCG.
Pituitary disorders
Some health conditions involving the pituitary gland can elevate hCG levels and cause a false positive pregnancy test. These include tumors of the pituitary gland or adrenal glands. High levels of hCG may also indicate testicular cancer in men.
Menopause
Perimenopause is the transition period leading up to menopause when periods become irregular. Fluctuating reproductive hormone levels during perimenopause can occasionally result in a positive pregnancy test even when not pregnant.
Medical conditions
Certain medical conditions may elevate or mimic hCG levels, leading to a false positive pregnancy test. These include gestational trophoblastic disease, choriocarcinoma, polycystic ovarian syndrome, uterine fibroids, and abdominal pregnancy.
Evaporation lines
As the urine sample on the pregnancy test kit evaporates and dries, it can leave a line that may look similar to a positive result. An evaporation line does not have any color to it unlike an actual colored positive line.
Chemical pregnancy
It’s possible to have an early miscarriage even before realizing you are pregnant. Known as a chemical pregnancy, hCG levels rise but then fall as embryonic development stops and no gestational sac formed. The positive test may detect the short-lived hCG rise.
Ovarian cysts
While uncommon, large ovarian cysts may secrete enough hCG to make a pregnancy test positive. Dermoid cysts and cystadenomas can sometimes produce hCG.
Contamination
Urine tests may rarely become contaminated with hCG from a nearby positive test. Using separate testing areas and washing hands in between tests helps avoid the possibility of contamination.
Risk factors for false positives
While any woman can experience a false positive pregnancy test, some circumstances or risk factors make them slightly more likely:
- Taking a pregnancy test too soon after fertility treatments with hCG
- Not following the test instructions properly
- Testing before your period is expected or missed
- Testing with an expired test kit
- Having a medical condition causing elevated hCG
- Going through the menopausal transition
- Taking medications containing hCG
How to avoid false positives
There are some simple tips that can help avoid a false positive pregnancy test:
- Take the test after missing your period, when hCG levels are highest
- Read and follow all test instructions carefully
- Check the test kit expiration date and do not use if expired
- Take the test first thing in the morning with concentrated urine
- Avoid excessive fluids before testing as it may dilute the hCG hormone
- Use a digital test kit instead of one reading lines
- Retest with a new kit to confirm if you get a positive result
Confirming pregnancy after a positive test
If you have received a positive pregnancy test result, the next advised step would be to schedule an appointment with your healthcare provider. A medical professional can use more sensitive quantitative blood tests to measure your exact hCG levels. Levels that rise appropriately confirm that the positive test result is indeed due to pregnancy. Ultrasound around 5-6 weeks can also provide visual confirmation and check that the pregnancy is progressing normally.
Emotional impact of false positives
Thinking you are pregnant when you are not can be an emotional rollercoaster. You may feel excited at the prospect of having a baby only to then feel disappointed and sad. Some women need support to cope with the psychological effects of a false positive. Talking to your partner, a friend or a counselor can help process these emotions. Know that false positives are rare fluke results and not your fault.
Key takeaways
- False positive pregnancy tests are very uncommon but can still happen.
- Too early testing, fertility treatments, and some medical conditions can cause extra hCG.
- Home pregnancy tests are over 99% accurate when directions are properly followed.
- Retesting with a different test kit can help confirm an initial positive result.
- See your doctor for hCG blood tests and ultrasound to get confirmation.
Conclusion
While false positives on home pregnancy tests are rare, they do occasionally happen for various reasons like medication effects or medical conditions causing abnormal hCG production. Using tests as indicated and retesting for confirmation is wise. If you do receive a positive pregnancy test result, make an appointment with your doctor right away to have the pregnancy properly evaluated through quantitative hCG blood tests and ultrasound. This will provide definitive confirmation and help determine next steps for prenatal care.
