False positive pregnancy test: 6 reasons why it happens

False positive pregnancy tests are very unusual but DO happen: find out what causes a false positive - when a test shows you’re pregnant but you're not

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It is possible to have a positive pregnancy test result and not actually be pregnant – despite many people telling you otherwise. It’s called a false positive – and while it’s not common – it does happen (and we know it can be seriously disappointing if you’re trying to conceive ? )

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It can be for a number of reasons: maybe you were pregnant but are no longer, or perhaps there was a fault with how the test was done / the test was out of date.

“A false positive result is very rare,” explains midwife Anne Richley of Northampton General Hospital Trust (NHS), “but may occur for a few possible reasons,” – some of which we’ve mentioned above and will go through in this article.

We know they do happen because there’s a fair bit of chat on this topic on our forum – take New_here, who says: “I’ve recently taken 4 First Response tests (6 days before [ovulation]).

“They were all positive but then I went and took another 5 (different brands) – all negative – so took another First Response and positive? Went to the doctor’s – negative?! So confused – could I be getting false positives?”

What causes a false positive pregnancy test?

While, as we’ve said, false positives are rare, they happen occasionally. On our forum, Annie Mac tells us: “I just want all you ladies who are crossing your fingers and toes to remember that false positives DO happen.

“If you do get a positive it is very likely you’re pregnant due to false positives being very rare. I was having all the pregnancy symptoms and took a Planned Parenthood HPT test and BOOM bright positive! It turned out it was false and got my hopes up for nothing.” 

So why do they happen?

False positive pregnancy test result – reasons you might get one

1. You were pregnant, but you aren’t pregnant anymore

As what happened with New_here above, a pregnancy may initially be detected by an early pregnancy test, which will give you a positive result. But then, when you test again at a later time, you get a negative result.

Which one is right? Unfortunately the later negative result is more likely to be the true situation – that you’re no longer pregnant.

It doesn’t mean the first positive test was wrong. It was just an early test which detected the first stages of pregnancy.


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Sadly, many pregnancies don’t make it beyond these first few weeks. Improvements in pregnancy tests mean that they’re now highly sensitive and can detect the first stages of pregnancy super early.

A later negative test could mean your pregnancy unfortunately hasn’t continued and you’ve experienced an early miscarriage.

This is also known as a chemical pregnancy – a (slightly insensitive) term which means that your pregnancy was in the very early stages and had been detected by a chemical (pregnancy) test, but then hasn’t progressed.

2. The test wasn’t done correctly

If you read your pregnancy test after the suggested time, a faint evaporation line may develop. (Got one? Find out what  else a faint line on your pregnancy test could mean.)

This is not the same as a positive test. This is why it’s so important to check the instructions for how to use your test correctly.

3. The pregnancy test kit was out of date

If you’ve had an unused pregnancy test for a long time, check the expiration date on the packaging. These are sensitive chemical tests and need to be in date to ensure they’re working correctly.

4. You may be having fertility treatment involving hCG hormones

Your home pregnancy test measures the levels of hormone hCG in your urine, looking for the sharp increase in hCG when you become pregnant.

Some fertility drugs contain hCG, and so it’s wise to check this before you test. Clomid, which is a popular fertility drug, does not contain hCG and so does not have an impact on your home pregnancy test result.

On our forum, StrawberryGirl went to her doctor to find out more. “I spoke to the doctor when I couldn’t believe that I was pregnant.

“You very, very rarely can get false positives though this can happen if you have been on fertility treatment.”


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5. You’ve recently given birth and your hCG hormone levels are still high

StrawberryGirl goes on to say that the doctor told her when you have a baby your levels of hCG may still be higher than normal. “You will also get a positive just after you have given birth as the hormone hCG still in your system,” she reveals.

So, you’re testing soon after giving birth, talk to your doctor.

6. It may indicate an unusual medical condition

It’s important to know that this is very, very rare. However, there are certain illnesses which cause an increase in hCG, such as trophoblastic disease or islet-cell tumours. If you’re at all concerned, talk to your GP.

If you’re worried because you can only see a very faint line on your pregnancy test, but have done everything correctly, this sounds like a positive result.

If you remain unsure about whether or not you are pregnant, do visit your GP who will test again and be able to give you advice on what to do next.

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