PREGNANCY

Positive pregnancy test followed by negative: what's going on?

Last modified on Wednesday 12 April 2023

If you got a positive pregnancy test result and then took another test and got a negative result, you're probably confused and wondering what's going on! Read on as we shed some light ...

If you have taken a pregnancy test and got a positive result and then taken another test but got a negative result you're probably thinking – what's going on?

There are many reasons women take a second test, from not feeling confident about a faint line to wanting to be absolutely certain before they share their good news with friends and family.

It's common for women to take a second and even a third test if they're not sure about the results.

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In this article we'll look at how pregnancy tests work and 5 reasons why you might get a negative result after a positive one.

How pregnancy tests work

You might already know how pregnancy tests work, but it's always helpful to have a recap.

Home pregnancy tests detect hCG levels in your urine. Human chorionic gonadotrophin (hCG) is also known as the pregnancy hormone. It is produced by the placenta shortly after the embryo implants in the uterus.

It takes time for hCG levels to build up in your system, which is why you have to wait for at least 2 weeks before you can take a pregnancy test. The NHS says, 'Pregnancy tests are most reliable from the first day of your missed period.'

This is because it takes about 6 days after conception for your body to produce the pregnancy hormone and then another few days after that for the level to be high enough to be recognised by a pregnancy test.

If you take a pregnancy test before you've missed a period, you're more likely to get an inaccurate result.

Different tests have different levels of sensitivity, however, so you may be able to take some tests earlier than others. 'Some very sensitive pregnancy tests can be used even before you miss a period,' the NHS says. Always read the instructions carefully to avoid inaccurate results.

Find out more about how soon you can take a pregnancy test.

Once you've taken the pregnancy test, your results will show up in the window as 1 or 2 lines. These will appear either side-by-side or overlapping to form a 'plus' sign. It could also be a digital readout saying 'pregnant' or 'not pregnant', produced by a mini computer inside.

More expensive tests can even tell you how many weeks pregnant you are!

5 reasons why a positive pregnancy test could be followed by a negative one

'Home pregnancy tests are accurate as long as you follow the instructions correctly. A positive test result is almost certainly correct. However, a negative test result is less reliable,' according to the NHS .

In reality, results are not always that straightforward though. If your first positive result was faint or you just wanted to be sure before you shared your good news, you may have decided to take another test, but this time the results are negative!

So what's going on?

Here are some possible causes of getting a positive pregnancy test result followed by a negative one ...

1. Chemical pregnancy

Chemical pregnancies are far more common than many women realise. (Other women have shared their experiences of chemical pregnancies in the Netmums Forum .)

They occur when an egg has been fertilised and implants into the uterus lining, but sadly it doesn't develop properly and leads to a miscarriage .

Most women don't even realise that they've had a miscarriage this early on because, although bleeding and cramping can occur, it is often mistaken for a heavy period. Chemical pregnancies usually happen before the fifth week of pregnancy.

If you took a pregnancy test that gave a positive test result initially and then after taking a second one you get a negative result, you may have indeed experienced a chemical pregnancy. This means the second test is correct and you're not pregnant anymore.

2. Evaporation line

If you're second test is negative after a positive result, you may have mistaken an evaporation line in the first test as a positive result.

Sometimes pregnancy tests can display a faint second line, which could be a faint positive or it could be an evaporation line. The difference is that an evaporation line is colourless and is a negative result.

Evaporation lines usually occur when the test is left too long before reading the results, and the urine has started to evaporate. Evaporation lines have no colour because the dye hasn't bonded to the urine. Therefore the result is negative.

That's why the instructions on pregnancy tests say to read the results on your test within the time-frame specified. Otherwise they may be inaccurate.

Don't assume you know how to take a test without reading the box. It's always important to read and follow the instructions carefully as different pregnancy tests may vary in the way that they work.

3. Diluted urine

Women are often advised to take a pregnancy test first thing in the morning. This is because urine is most concentrated before you have had anything to eat or drink.

If your urine is diluted because you have taken a pregnancy test later on in the day or after consuming liquid you may get a false negative result. This is because the pregnancy test is less likely to pick up on the lower levels of hCG in the urine

For best results always try to use your first urine of the day when taking a pregnancy test.

4. Ectopic pregnancy

An ectopic pregnancy happens when the fertilised egg implants outside of the uterus. In most cases the fertilised egg implants in the Fallopian tube. It's a very serious condition that could be life-threatening and requires emergency treatment, according to the Cleveland Clinic.

It's tricky because the symptoms of an ectopic pregnancy are like those in a typical pregnancy. Other symptoms include bleeding, dizziness or abdominal or lower back pain. If the fallopian tube ruptures, you could feel a sharp pain that causes fainting, bowel problems or more.

With ectopic pregnancies you may initially get a positive pregnancy test result. But later tests may show negative results. If you are at risk of ectopic pregnancy or are concerned you might have one, get in touch with your doctor immediately.

5. Faulty pregnancy test

If you took two tests and they are showing different results, it might be that one of the tests is faulty and has given you inaccurate results.

Of course, you won't know which one is the faulty one, so you'll have to take another test to be sure.

Fault pregnancy tests can be the result of:

  • a manufacturing defect
  • issues with the storage or handling of the kit
  • the pregnancy test may be expired

Always check the expiry date on the box before you buy or use a pregnancy test.

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