What causes a false positive pregnancy test?

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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While understanding the intricacies of pregnancy tests, it’s also essential to address common concerns that might arise during this period, such as the potential impact of urinary tract infections (UTIs) on pregnancy test results.

Exploring UTIs and Pregnancy Test Accuracy

UTIs, while uncomfortable, typically do not interfere with the accuracy of pregnancy tests. These tests are specifically designed to detect the hormone hCG, which is unique to pregnancy. Therefore, the presence of bacteria or leukocytes, which are common in UTIs, does not mimic hCG and should not lead to a false positive result.

Addressing Common UTI Concerns:

• Impact on Pregnancy Tests: Despite myths, there is no scientific evidence to support that UTIs can cause false positive pregnancy test results. The specificity of home pregnancy tests to the hCG hormone ensures that factors like bacteria or blood in the urine, common in UTIs, do not affect the outcome.
• Ensuring Accurate Results: To mitigate any concerns about the accuracy of your pregnancy test while dealing with a UTI, it’s crucial to follow the test instructions meticulously. Using the test correctly and within the recommended time frame helps ensure reliable results.
• Health Considerations: If you suspect you have a UTI, seeking medical treatment is important, particularly if you are pregnant or attempting to conceive. While UTIs do not influence pregnancy test outcomes, they require prompt attention to avoid complications.

Professional Guidance is Key

Regardless of home pregnancy test results, consulting with your healthcare provider is a vital step. This is especially true if you’re experiencing symptoms of a UTI. Your provider can confirm your pregnancy status and address any urinary tract infections, ensuring both your health and the health of your pregnancy are monitored and supported.

By understanding the relationship between UTIs and pregnancy tests, you can navigate this aspect of early pregnancy with greater confidence and clarity. Remember, while UTIs are a common concern, they don’t impact the reliability of pregnancy tests. Prioritizing your health and seeking professional guidance are your best strategies for navigating early pregnancy and any concerns that arise during this transformative period.

FAQ: Understanding Pregnancy Tests and UTIs

Can a UTI cause a false positive on a pregnancy test?

No, a urinary tract infection (UTI) does not cause false positive pregnancy test results. Pregnancy tests are designed to detect the hormone hCG, which is specific to pregnancy. The presence of bacteria or leukocytes in urine from a UTI does not mimic hCG.

Why is there concern that UTIs can affect pregnancy test results?

The concern might stem from the misunderstanding that substances present in the urine due to a UTI, such as proteins or blood, could interfere with the test’s detection of hCG. However, pregnancy tests are highly specific to the hCG hormone, making such interference highly unlikely.

What should I do if I have a UTI and get a positive pregnancy test result?

If you have a UTI and receive a positive pregnancy test result, consult with your healthcare provider. They can confirm your pregnancy through additional testing and provide the necessary treatment for the UTI, ensuring both your health and the health of the pregnancy are taken care of.

How can I ensure accurate pregnancy test results while having a UTI?

To ensure the most accurate results from a home pregnancy test while having a UTI, follow the test instructions carefully, especially regarding the timing for reading the test. Consider confirming the results with a healthcare provider.

Are UTIs common during pregnancy?

UTIs can be more common during pregnancy due to changes in the urinary tract. The expanding uterus can put pressure on the bladder, making it easier for bacteria to enter and cause an infection. Regular check-ups can help identify and treat UTIs early in pregnancy.

What are the risks of a UTI during pregnancy?

If left untreated, UTIs can lead to more serious infections and may increase the risk of preterm labor. It’s important to seek treatment promptly to avoid any complications.

Can I take a pregnancy test if I’m currently being treated for a UTI?

Yes, you can take a pregnancy test while being treated for a UTI. The treatment for a UTI, which often includes antibiotics, should not affect the outcome of a pregnancy test. However, always follow up with your healthcare provider for confirmation and further guidance.

A version of this story was originally published on June 3, 2021. It has been updated.