Are false positives common in pregnancy tests

No matter what, taking a pregnancy test can be an emotional roller coaster. When it comes to getting a false positive pregnancy test result, the experience can be deeply upsetting, particularly for anyone who has had a difficult time getting pregnant or is actively hoping to get pregnant (or both). The hope that comes with seeing that positive sign crashing down as you realize it was a false positive pregnancy test? It's a uniquely devastating emotion. 

Of course, getting a false positive pregnancy test when you’re actively trying not to get pregnant can be just as horrible. Yup, you could probably do without the panicked verification trip to the ob-gyn, just to learn there was nothing to stress over. 

Thankfully, experts note that false positive pregnancy tests are rare. Unfortunately, though, they can happen. Here are some of the most common causes of a false positive pregnancy test, along with some additional information that can help you put it all into context.

First, what is a pregnancy test?

Let's start with the absolute basics just to make sure we're all on the same page. A pregnancy test tells you if you’re pregnant or not. That's simple enough to understand. But it's understandable if you're a little fuzzy on the details of what these devices actually look for to identify a pregnancy.

At-home pregnancy tests check for the hormone hCG. HCG is short for human chorionic gonadotropin, which the body creates during pregnancy. Right after a fertilized egg attaches to the uterine lining, the placenta then forms and starts producing hCG1. A blood test can detect hCG about nine days after conception, and a urine test can detect it 12 to 14 days after conception, according to the Cleveland Clinic, although it varies—some especially sensitive urine tests can detect a pregnancy even earlier. A person’s hCG level typically doubles every 72 hours through 8 to 11 weeks of pregnancy. Then it remains consistent and starts to go down after delivery.

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How does a pregnancy test work?

An at-home pregnancy test is designed to find hCG in pee2. If the hormone is present, it triggers a chemical reaction and the test signals that you're pregnant. If hCG is not present, the test will say you aren't pregnant. Many tests use two lines to mean you’re pregnant and one line to mean you’re not—but it depends on the test brand. Some tests use plus and minus signs. Some digital pregnancy tests have a screen that plainly reads "pregnant" or "not pregnant." Which can save you some “Is that one line or two?!” squinting, at least.

Seems simple, right? As Ina Garten would say, "How easy is that?" Typically, pretty easy. Most at-home pregnancy tests claim to be about 99% accurate3. Ultrasounds typically can't detect a pregnancy until a little later in your pregnancy and that's why at-home tests are so useful. But, sometimes, other elements can mess with a pregnancy test's results and tell you you’re pregnant when you’re really not. 

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What can cause a false positive pregnancy test?

Here are the most likely reasons you may end up with a false positive pregnancy test:

1. You let the test sit too long before looking.

If you take a standard pregnancy test with line indicators, it's important to check the results according to the specific instruction of the test. If you let it sit too long before reading the results, urine on the test can evaporate and make it look like you have two lines instead of just one. "Oftentimes people will see evaporation lines as urine starts to evaporate off the test," Jamil Abdur-Rahman, M.D., board-certified ob-gyn, tells SELF. That might cause the test to look like it has a faint second line—making it positive—but it really only has one.

The best way to avoid this: Read the pregnancy test's directions and follow them exactly. The popular pregnancy test brand First Response, for example, instructs users to wait three minutes after taking the test, then read it as soon as possible4.

2. The pregnancy test is expired.

The second most common reason Dr. Abdur-Rahman's patients get false positives is because the test is expired, he says. When a test is past its expiration date, the chemical that detects hCG doesn't always work as it should, and you’re more likely to get a misread. "The test can expire and the chance of having a false positive increases," Dr. Abdur-Rahman says.

3. You’re on fertility medications that raise hCG levels.

If you take a pregnancy test too soon after taking a fertility drug that contains hCG—like some injections that are often part of in vitro fertilization—you could get a false positive.

If you're taking a pregnancy test, you want to be sure you can trust the results. Thankfully, the vast majority of the time, when you take an at-home pregnancy test your result will be accurate. In fact, studies show that when done correctly, these tests are around 99% correct.

However, while a false positive pregnancy test result is uncommon, it can happen, for a variety of reasons. Learn more about the causes of false positive pregnancy tests.

What Is a False Positive?

A false positive on a pregnancy test means that the test result says you are pregnant but you actually aren't. In most cases, this means the test detected the hormone hCG in your urine when there really was no hCG in your urine. However, sometimes, there may be hCG in your urine even if you are not (or are no longer) pregnant with a viable embryo.

The newer, more sensitive early pregnancy tests can detect lower amounts of hCG in the urine, making them more sensitive, and in rare cases, they can indicate pregnancy when one does not actually exist. Though there are reasons why you may have a false positive.

Causes

There are a variety of reasons that a home pregnancy test may have a false positive result. For a false positive to be shown on your pregnancy test, you either have hCG in your body for some other medical reason or the test was not working correctly.

Call your doctor or midwife for advice on what to do if you get a positive result but then discover that you're not pregnant. They may wish to do blood work to see if hCG is found in your blood or do other testing to rule out any other health issues.

Test Error

While rare, the home pregnancy test you are using could be faulty. Some reasons include if the test was not stored properly and was damaged by heat or water. Or there could be a defect due to a manufacturing issue, but again, this is rare.

More likely, although still uncommon, the error could be due to taking the test incorrectly. For example, you could have waited too long to read the results or you could be misinterpreting the test strips, which sometimes have faint lines, called evaporation lines, that can show up for negative results. True positive results will show up as bright lines.

Early Pregnancy Loss

Another possibility is that you had a correct positive result, in that hCG was found, but that the hCG levels are falling. This is not technically a false positive in the sense that it did detect hCG, but it is false in the sense that you may not have a viable pregnancy. This lower hCG may be a sign of a miscarriage or chemical pregnancy, which is when an embryo doesn't implant or grow. You may also still have hCG in your body after a recent abortion.

Ectopic Pregnancy

You can get a positive pregnancy test result with an ectopic pregnancy, which is also known as a tubal pregnancy. An ectopic pregnancy is when an embryo implants outside of the uterus. Unfortunately, these pregnancies are not viable and treatment is required to remove the embryo to protect the health of the pregnant person—and their fertility.

Symptoms of ectopic pregnancy include dizziness, vaginal bleeding, fainting, rectal pressure, and/or abdominal, pelvic, or shoulder pain, If you experience any of these symptoms along with a positive pregnancy result, contact your doctor.

Some Medical Conditions

There are a variety of medical issues that may cause a false positive result. For example, a positive pregnancy test can sometimes indicate a molar pregnancy, a type of non-cancerous tumor that's also called also known as a hydatidiform mole. Other possibilities include having a urinary tract infection, certain types of ovarian cancer, and kidney disease.

Certain Medications

Some medications may create a false positive pregnancy test result as well. These include some anticonvulsants, anti-anxiety drugs, antihistamines, diuretics, chemotherapy medications, antipsychotics, drugs that treat Parkinson's disease, and methadone.

Pregnancy Confirmation Visit

If you get a positive pregnancy test, it's always a good idea to follow up with your doctor. Most doctor's offices use urine tests to test for pregnancy that are very similar to what you use at home. Though they may not look the same, the technology is essentially the same.

If they think that there is an issue with the urine test you used at home, they may opt to try a urine test in the office, or they may go straight to a blood pregnancy test. This would usually then be repeated to tell what the exact hCG numbers were and whether it was going up or down in the two tests. This can give you a better idea of if you had a false positive or if it was a fluke from the test itself.

What Happens If You Have a False Positive Test Result?

If you have had a false positive on a pregnancy test, that means you are not pregnant. If another medical condition caused your false positive result, you may need treatment. If not, you may decide to try to get pregnant. Or you may even find out later in this cycle that you are pregnant, but just weren't pregnant enough at the time of the original test.

"I had a slight positive pregnancy test and went to the doctor," says Clare. "I was really surprised when they said I wasn't pregnant. I felt a bit foolish. Turns out two weeks later, I really was pregnant. One urine test was right, the other wrong."

However, for many people, it may take several cycles to become pregnant. If you have been trying for a year (or for six months if you're 35 or over), consult with your OB/GYN to have your fertility evaluated, if needed.

A Word From Verywell

While unlikely, getting a false positive pregnancy test result is possible. If you're trying to conceive, it can be very upsetting and confusing to think you're pregnant only to discover that you're actually not. Talk to your doctor if you have any questions about your fertility and the best way for you to get pregnant and test the next time you suspect you might have conceived.

Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. Gnoth C, Johnson S. Strips of hope: accuracy of home pregnancy tests and new developments. Geburtshilfe Frauenheilkd. 2014;74(7):661-669. doi:10.1055/s-0034-1368589

2. Valenzuela R, Iserson KV, Punguyire D. False-positive urine pregnancy tests--clinicians as detectives. Pan Afr Med J. 2011;8:41. doi:10.4314/pamj.v8i1.71156

3. Eskandar MA, Al-Shahrani M, Shaamash A, El-Emain M, Al-Ahmad M, Payodon B. Early Maternal Serum β-human Chorionic Gonadotropin Measurements After ICSI in the Prediction of Long-term Pregnancy Outcomes: A Retrospective Cohort Analysis. J Clin Med Res. 2011;3(1):30-5.  doi:10.4021/jocmr477e

By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.

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