You've taken your pregnancy test, and it was negative. But when you go back to it later or see it when you clear out the bin, there's a line! What gives?

Whether the Two Week Wait is finally over, you're doing a pregnancy test a bit early because you just can't wait or you're late for your period and just double-checking, using a pregnancy test can be a nervy experience.

So what does it mean if your negative result somehow has turned into a positive one later on? Unfortunately, one way or another, it's a sign that something has gone wrong with the test. Read on to find out more about why this might happen.

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That's why the instructions on pregnancy tests tell you to look at the results within a certain time frame. If you look too late, you can end up with evaporation lines, which can trick you into thinking you have a positive result.

What it comes down to is: if your test said that you were not pregnant during the time window for taking a reading, then it is still negative EVEN IF you see a line after that time .

What a false negative on a pregnancy test?

That said, you can get what's called a 'false negative' on pregnancy tests. A false negative occurs when it's just too early to tell if you're pregnant. Pregnancy tests measure the levels of pregnancy hormone hCG (human chorionic gonadotropin) in your urine and if the hCG hasn't built up enough to register on a test, the your test will be negative.

If you want to be sure, wait a few days and test again.

Why did my pregnancy test change from negative to positive?

There could be several reasons why your pregnancy test results go from negative to positive.

• It's most likely because you're reading the test after the recommended time. Most pregnancy tests will tell you to take your reading between 2 and 10 minutes after you pee on the stick, and if you read it after that the results are invalid.
  That's because after a while the urine on the test will evaporate, leaving what's called an evaporation line. Unlike a positive result which will have a small amount of the red or blue dye the test uses to show them, evaporation lines are faint and colourless. They can quite easily be mistaken for a faint positive line , which could lead you to think that your result has changed from negative to positive.
• Another reason why you could end up with an evaporation line is if you accidentally splashed a bit of wee onto the results window when you were first using the stick.

Either way, if you checked your test within the time that the instructions said to and it was negative, then you are probably not currently pregnant .

If you think it could just be too early to test , depending on when you last ovulated and when conception occurred, wait a few days or a week then test again.

If you would like more information about pregnancy tests and how they work, take a look at the stories below. You can also head over to our Forum to talk to other parents and hopeful parents for support and answers.

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