Can a negative pregnancy test turn positive after sitting

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.

Taking a pregnancy test is relatively straight forward: you pee on a stick and then it shows you whether you are pregnant. But what if your pregnancy test results change in a matter of a few hours? What can cause that?

In this article:

• How Do Pregnancy Tests Work?
• Why Did My Pregnancy Test Results Change From Negative to Positive in Several Hours?
• How Can I Avoid Incorrect Pregnancy Test Results?
• Ultimately…

Before we find out what can cause a pregnancy test result to change from negative to positive over a few hours, we must first understand how pregnancy tests work.

How Do Pregnancy Tests Work?

Home pregnancy tests are accurate tools used for detecting pregnancy.

Pregnancy tests work by testing your urine for the presence of a hormone called human chorionic gonadotropin (hCG).

The hCG hormone begins to be produced after implantation occurs- the process where a fertilized egg implants into the lining of your uterus. It is through this connection, that the fertilised egg (or blastocyst) receives the nutrients and blood supply it needs to grow.

If your hCG levels are high enough in your urine (usually around 2 weeks after conception), the pregnancy test will dispaly a positive result.

Positive pregnancy test results can be shown by a cross, two lines (a test line and a control line), or even the word “pregnant”- depending on the kind of pregnancy test you choose.

But what can cause pregnancy test results to change? Read on to find out..

Why Did My Pregnancy Test Results Change From Negative to Positive in Several Hours? – 4 Reasons Why

1) You Left Your Test For Too Long

It is important to always follow the pregnancy test instructions, as not following the pregnancy test instructions, or following them incorrectly, can give you incorrect pregnancy test results.

Pregnancy test results are only valid for a certain amount of time- usually around 10 minutes- so if you leave your pregnancy test out for several hours, and notice that your negative test result has changed to a positive test result, you should just disregard the changes, as they are most likely inaccurate.

This is because, over time, the urine within the result window begins to dry- which causes an evaporation line (faint line) to appear. This can easily be mistaken for a faint positive pregnancy test result.

2) Your Urine Was Diluted

During early pregnancy, if you have taken a pregnancy test and received a negative result, and took another pregnancy test and received a positive pregnancy result several hours later, it may be due to the amount of fluids you are drinking.

If you drink a lot of fluids, it can dilute your urine- decreasing your hCG levels in your urine, which can cause a negative pregnancy test result to be shown.

3) Evaporation Line was Mistaken for A Faint Positive Result

Evaporation lines can be pesky things! They can look like a positive faint test line, whilst they are not a positive result at all!

Evaporation lines are the product of the urine drying on the home pregnancy test, which causes the results window to show a faint line.

If you are unfamiliar with evaporation lines, you may mistake them for a positive test line.

4) It Was A False Positive Result

It may be that the pregnancy test result you received later on in the day may have been a false positive. False positive pregnancy test results are caused by a variety of things, including:

• Following the pregnancy test instructions incorrectly
• Using an expired pregnancy test
• Using an unreliable brand
• Other unknown reasons.

How Can I Avoid Incorrect Pregnancy Test Results?

• Check the Expiry Date. If you are taking a pregnancy test, it is important to make sure that the pregnancy test has not expired. Once a pregnancy test expires, the antibodies within pregnancy test, which detect the hCG, begin to break down. This can cause a negative result to be shown, when you are actually pregnant.
• Follow the instructions carefully. Following the pregnancy test instructions carefully is crucial to receiving accurate test results. It is important to note whether you should take a urine sample and dip the pregnancy test, pee directly onto the pregnancy test, when you should read the results, and when the results should be rejected.
• Take the pregnancy test in the morning. Taking a pregnancy test with the first morning’s urine can help you to receive the most accurate pregnancy test results- this is because your hCG levels are the most concentrated, so if you are still in early pregnancy, you are more likely to receive a true positive test result.
• Wait until your hCG levels are high enough. We know how difficult the two week wait can be- however, it is there for a reason! Taking a pregnancy test kit too early can give you a negative result, even when you actually are pregnant!

Ultimately..

Ultimately, if you are unsure of your pregnancy test results, you should take a test again in a few days time to avoid inaccurate results. If you received a positive test result and then negative 2 hours later, we have an article on that too which you can read.

Hi, I’m Louise- mum of one to a little boy called Mason.

I am the Digital Marketing and Admin Assistant for MyBump2Baby.

I enjoy working to provide excellent service to MyBump2Baby’s growing families.

Nice to meet you!

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