From the moment you see those two little lines on a pregnancy test, you may experience a rush of emotions. And waiting for a doctor’s visit to confirm the news can feel like torture.
Many women choose to take a second (or third!) at-home test. Occasionally, though, those tests may have different results.
What does it mean when one pregnancy test is positive and the other is negative?
While many home pregnancy tests promise a 99% accuracy rate, they’re not perfect. Occasionally, ‘false positives’ occur—when you get a positive result, even though you’re not actually pregnant.
We’re breaking down everything you need to know about false positive pregnancy tests.
Are false positives common?
Thankfully, no.
“False positives are fairly unusual,” says Mary Jane Minkin, M.D. and Clinical Professor of Obstetrics at Yale School of Medicine. “Among the more common explanations are women who wait longer than the recommended time to read tests, and with evaporation, another line can appear (which is not a true positive, but just a function of the test sitting there for more than the recommended time.)”
Related: What does a faint line on a pregnancy test mean?
Can medications cause a false positive?
It’s possible. “Fertility drugs or other medications that contain HCG might interfere with home pregnancy test results,” says the Mayo Clinic. “However, most medications, including antibiotics and birth control pills, don’t affect the accuracy of home pregnancy tests.”
What else could cause them?
A serious urinary tract infection (UTI) can cause a false positive, according to Gloucestershire Hospitals.
Or it could be related to changing hormone levels. “Occasionally, especially given the sensitivity of these tests, the test could stay positive for a few days, and then turn negative,” adds Dr. Minkin. “What that can signify is something that folks call a chemical pregnancy. Indeed, an egg was successfully fertilized, started to implant and then stopped developing, and what will happen then is the early pregnancy will pass out from the uterus. It may just seem like a heavy period a few days late. It is really a very early miscarriage. So, the pregnancy test was not a false positive.”
“Knowing that you could get pregnant is really a very positive thing—the sperm made it through to meet up with the egg, and fertilization took place. In general, what causes the very early miscarriage is that particular sperm meeting up with that particular egg. They didn’t end up perfect genetically, and the embryo stopped developing—but that should have no bearing on you conceiving subsequently—and you know you could get pregnant,” she says.
Related: The new mama’s guide to pregnancy symptoms
Is there anything you should do to make sure you don’t get a false positive?
The easiest way to avoid them is to read the test in the suggested timeframe, says Dr. Minkin.
And remember: they’re really not that common. If you’re feeling anxious, you can repeat the test in a few days.
Related: A nutritionist’s guide to the best foods for pregnancy, from the early days to the third trimester
What should you do after getting a positive test reading?
First, make sure you book an appointment with your healthcare provider to confirm the results.
While you’re waiting for that appointment, Dr. Minkin recommends starting a prenatal vitamin with extra folic acid. “Pregnancies that are conceived while the woman is on extra folic acid have a lower chance of having neural tube defects and other congenital anomalies,” she says.
If you’re not actually pregnant, a prenatal vitamin won’t hurt you. And if you are pregnant, your baby will benefit from the early folic acid.
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A version of this story was originally published on June 3, 2021. It has been updated.
False positive pregnancy tests are rare. This is because the accuracy of pregnancy tests is extremely high. But, no matter how high the accuracy rate, there is a slim chance of an incorrect result being given from time to time. In most instances, this is a result of human error. Other times, there are medical conditions that can alter results. And one of those conditions that can cause a false positive pregnancy test result is a urinary tract infection.
Most at-home pregnancy tests have an accuracy rate of 99 percent. This means that as long as women follow the instructions, have waited the correct amount of time to test, and do not wait too long to read the results, the readings the test gives will be on point.
But there are rare occasions when tests are incorrect. And this is why when women receive a positive pregnancy test reading that doctors test with not only another pregnancy test but a blood test as well to confirm women are truly expecting.
Here is how a UTI can cause a false positive pregnancy test.
What Is A Urinary Tract Infection?
via Pexels/Andrea Piacquadio
In most instances, a urinary tract infection is caused by a bladder infection, according to WebMD. It occurs more often in women than men.
When a UTI is present, it is the result of E. coli making its way into the urinary tract. And when this happens, multiple areas of the body are infected.
The areas of the body that are infected, per the publication, include:
- Kidney
- Bladder
- Ureters
- Urethra
If treatment is delayed, the bladder infection can easily travel to other areas of the urinary tract. Infections in the ureters and kidneys are much more painful and take more time to treat, according to WebMD. And because of this, it is recommended to get treatment right away while symptoms are still mild.
Signs Of A Urinary Tract Infection
via Pexels/Sora Shimazaki
When women are suffering from a urinary tract infection there are clear signs and symptoms that that is what is being experienced.
According to American Family Care Urgent Care, the symptoms of a UTI include:
- Blood in urine
- Burning sensation when urinating
- Cloudy looking urine
- Tiredness
- Fever
- Bad smelling urine
- Having to use the bathroom frequently
- Bladder pain
- Irritation in the vagina
If these symptoms are present, women can anticipate that they will be diagnosed with a UTI. And because a UTI will not go away on its own, once women believe they have one, they should seek care as soon as possible.
How A Urinary Tract Infection Can Cause A False Positive Pregnancy Test
via Pexels/Tima Muroshnichenko
As a result of having a urinary tract infection, it is possible to receive a false positive pregnancy test. It does not happen often, but it is one of the conditions that can cause incorrect results to occur.
According to Gloucestershire Hospitals, a false positive pregnancy test can result when women have a UTI because there is too much urine flow being put on a test at one time. This can cause the result to be diluted and give a result that is incorrect.
As such, when women believe they have a UTI and want to take a pregnancy test, they should pee into a cup to catch the urine. By placing the test into the cup, there will not be too much urine being placed on the stick and a correct result should occur.
Source: American Family Care Urgent Care, WebMD, Gloucestershire Hospitals