It is natural to second guess something as life-changing as a pregnancy test can be. So, can you get a false pregnancy test? There are several reasons why your test may not be as accurate as you thought. As much as five percent of all pregnancy tests report false-negative results.1
We spoke to Dr. Jessica Ryniec of CCRM Fertility Boston, MD Reproductive Endocrinology and Infertility, to understand what can cause false-negative and positive pregnancy tests.
How to Take and Read a Pregnancy Test
Before we address the causes of potential false positive and false negative pregnancy tests, we should cover how to take a pregnancy test. For the best chance of accurate results from a pregnancy test, wait 1-2 weeks after missing your period before testing and use urine from your first-morning pee.2
- Remove the plastic cap covering the absorbent window.
- Sitting on the toilet, begin to urinate.
- Place the absorbent tip underneath your stream of urine for 8 to 10 seconds.
- Alternatively, urinate into a small clean cup and dip the test’s absorbent tip into your urine for about 10 seconds.
- Replace the cap and lay your test flat.
- After 5 minutes, check your results.
- Remember not to leave your test too long, as this may cause a false positive.
There are three possible outcomes for your pregnancy test results:
- Positive result (possibly pregnant): You’ll see two bands in the control window—a band for the control and the test. The bands may be slightly faded or dark; either case means that the test is positive as long as both bands are visible. Depending on the hormone level, the test line is frequently lighter in color than the control line.
- Negative result (not pregnant): only the control line is visible, and there is no colored band in the control window’s test region.
- Invalid test: if no control line is visible, regardless of whether the test line is visible, this test is invalid. Repeat with a new test.
Causes of False-Positive Pregnancy Tests
First, it’s essential to be sure your pregnancy test is free of user error. According to Ryniec, common user errors with pregnancy tests are:
- Not checking the “control” window to ensure the test is functioning correctly.
- Using an expired test.
- Leaving the test too long with urine on it.
- Being on specific medications that can lead to a false positive (see below).
- Leaving your test at temperatures below 36° F or above 86° F.
- Storing tests where they will be exposed to moisture, heat, or direct sunlight.
The most common cause of a positive pregnancy test that doesn’t result in a pregnancy is a biochemical pregnancy. These pregnancies occur when sperm meets an egg, leading to an embryo that implants, but the pregnancy doesn’t progress. “Biochemical pregnancies can cause you to get your period just a few days to a week later than expected,” says Ryniec.
A similar cause of false pregnancy tests can occur when you experience an ectopic pregnancy. Ectopic pregnancies typically develop between the 4th and 12th week of pregnancy3, when a fertilized egg gets stuck on its way to your uterus, most commonly in the fallopian tubes. A fertilized egg cannot survive outside the uterus, leading to miscarriage. Ectopic pregnancies are rare, accounting for one to two percent of all miscarriages.4
It is important to note that while rare, ectopic pregnancies are a health risk that can cause organ damage and death.5 If you are concerned that you may be experiencing an ectopic pregnancy, speak to your health care provider immediately.
Signs of an ectopic pregnant include:
- Severe abdominal pain
- Pelvic pain with bleeding
- Shoulder pain
“You may also get a false-positive test if you are checking too soon after miscarriage or giving birth,” explains Ryniec. The pregnancy hormone hCG (human chorionic gonadotropin) level can stay elevated for up to six weeks after a miscarriage and can cause a false positive.
Medical conditions can also result in false-positive tests. Certain types of cancer, chronic kidney disease, or ovarian disease can cause false positives.
Finally, sometimes women can have high levels of pregnancy hormones after menopause, and these elevated hormones can cause a false-positive test.
Causes of False-Negative Pregnancy Tests
False-negative pregnancy tests are much more common than false-positive tests. The user errors discussed above are common causes of false-negative tests, for example:
- Taking the test too soon
- Not providing enough urine for a proper sample
- Not using morning urine when the hCG hormone is the most concentrated
- Using a damaged or expired test
- Medications that can cause false-negatives
Some Medications Can Cause False Pregnancy Tests
Since home pregnancy tests measure levels of human chorionic gonadotropin (hCG) hormone in urine, taking medication that contains hCG can cause a false-positive result.6
Drugs containing the hCG hormone that boost fertility may impact pregnancy test results. These may include:6
Other drugs that may cause a false positive pregnancy test include:6
- Antipsychotics often used to treat schizophrenia, such as perphenazine, prochlorperazine, chlorpromazine, trifluoperazine, thioridazine, and thiothixene
- The anti-seizure/anticonvulsant drug carbamazepine used for epilepsy, facial nerve pain, and bipolar disorder
- Progestin-only birth control pills, including:
- Anti-nausea drugs, including prochlorperazine, perphenazine, chlorpromazine, and promethazine
- Sedatives that are used before and after surgery or during labor, such as promethazine
- Antihistamines such as promethazine
- Anti-anxiety medications such as prochlorperazine and trifluoperazine
When in Doubt, Check With Your Doctor
At-home pregnancy tests have been on the market since 1976.7 Although using hCG as a marker for pregnancy is reasonably accurate, due to user error, faulty tests, and the possibility of failed pregnancies or medication causing inaccurate results, it may be necessary to visit your doctor to be sure of pregnancy.
Despite claims of tests being “over 99%” accurate, many over-the-counter pregnancy tests have not been tested in independent studies to prove their factual accuracy.
Tools such as ultrasounds can give a much clearer picture of whether your pregnancy test result is accurate.