3 positive pregnancy test and 2 negative

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.

by Polly Logan-Banks |

It's possible. Some home pregnancy tests are sensitive enough to detect tiny amounts of pregnancy hormones in your system, even before you have missed a period.

To get a positive result, you need to be making a detectable level of a pregnancy hormone called human chorionic gonadotropin (hCG). The more sensitive a pregnancy test is, the earlier it will show a positive result. It'll depend on how much hCG your body is producing too, as every woman's response to pregnancy is individual.

If your home test shows only a faint positive, it may not be sensitive enough to give you a clear answer. Check the side of the box to find out what your test's sensitivity is. For example, a test with a sensitivity of 10mIU/ml (milli-International Units per millilitre) will tell if you're pregnant sooner than a test with a sensitivity of 25mIU/ml.

You may get a faint positive because you're not as far along with the pregnancy as you expected. Sperm can live inside your body for up to seven days, waiting for an egg to be released. So depending on when you ovulate, you could get pregnant up to a week after having sex. Alternatively, your fertilised egg may not have implanted in your womb as quickly as expected.

Another possible explanation is what's known as an "evaporation line". This is a faint line that can appear as urine evaporates from the test, and it means you're not pregnant. The instructions that come with the test will tell you how long to wait before checking the results. If the faint line appeared a few minutes after this time, it's possible that it's just an evaporation line.

If you get a faint positive, you could try again using a digital pregnancy test. These are easier to interpret than a faint line, as they state whether or not you are pregnant. However, if you're testing early on, their accuracy still depends on the sensitivity of the test.

Alternatively, you could try taking another test in three days' time. If you are pregnant, and your body is making the normal amount of hCG, the test should be clearly positive by the time your period is due.

These early days while you wait to find out whether or not you are expecting can be an emotional rollercoaster. Unfortunately, it is possible to have a faint positive, only to get a negative when you retest a few days later.

If this happens to you, it may be that you have had a very early miscarriage. Sadly, miscarriages are very common, with a quarter of pregnancies thought to be affected. Learn more about early miscarriage.

One of the downsides of having such sensitive pregnancy tests is that, for some women, they may raise false hopes. When tests were not as highly sensitive to hormonal changes, very early miscarriages would simply go unnoticed. However hard it is, it may be sensible to wait until the day your period is due before testing. That way, you can be more sure of the results.

Still not sure what your faint line means? Get a second opinion (or two, or three…) by posting a photo of the test in our Line Eyes community group. Or learn more about pregnancy tests:

• Check out these 16 things you never knew about pregnancy tests.
• Discover seven things to remember when taking a test.
• Find out more about the best time to test.

Polly Logan-Banks is an experienced editor with a keen interest in producing evidence-based content. Polly is passionate about ensuring that every child gets the best start in life.

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