How accurate are pregnancy tests?

Woman looks at pregnancy test positive result

Whether you're trying to conceive or have just noticed some weird changes that you’re thinking could be early signs of pregnancy, there’s only one way to find out for sure – buy a pregnancy test and find somewhere private to POAS (pee on a stick).

How soon can you take a pregnancy test?

If your period's late and you're asking, “am I pregnant?” you might not have to wait long to find out. Most pregnancy tests can be done from the day your period is due. If your cycles aren’t regular or you don't know when ovulation happened, take a test 21 days after you last had unprotected sex.

Some newer types of pregnancy test are so sensitive they can be taken as early as eight days after conception, but be aware that if you get a negative result you won’t know for sure that you're not pregnant until after a missed period, so it's worth waiting as long as you can.

Which is the best pregnancy test?

You don't need to go to the GP to get a pregnancy test, but unfortunately you do need to do something a bit more scientific than an online pregnancy test or pregnancy quiz. Over-the-counter pregnancy tests are pretty accurate these days, but they do differ slightly in terms of how they work, how they display results and how sensitive they are – and therefore how soon you can use them. Here's the lowdown on some of the most popular pregnancy tests:

Clearblue pregnancy test

Clearblue claims 99% accuracy across all its products and offers a range of different tests to choose from, depending on what you’re after. If you like a bit of “data”, the Clearblue Digital With Weeks Indicator tells you in words if you are “pregnant” or “not pregnant” as well as how many weeks you are. It can be done up to five days before your period is due. Clearblue Digital pregnancy test

The Clearblue Early Detection test can be done up to six days before a missed period, if you're feeling impatient. And, if you're the sort who likes your pregnancy test with a bit of a drumroll, you could try Clearblue's Digital Test With Countdown for a Nasa-style 10 to zero to your result in words.

The company also does two tests with a change-colour tip so you can be sure you've hit the spot, as well as a “rapid results” test for the super-impatient.

First Response pregnancy test

First Response pregnancy test

The First Response Early Results test allows you to test up to six days before your missed period. Like the Clearblue products, it promises 99% accuracy from the expected day of your period. There's also a First Response Rapid Results test that will tell you whether you're expecting in less than a minute. (That's the results you'll get in less than a minute, not the baby, to be clear. No test is that clever.)

Asda pregnancy test

Asda Home pregnancy test

Asda's own Home Pregnancy test can be done up to four days before your period is due and also promises 99% accuracy on the day of your period – accuracy will be lower before. It doesn't have any fancy bells and whistles but retails at a much more wallet-friendly price, so if you're the sort to want to do 20 tests, just to be Absolutely Sure, you can indulge that need.

Boots pregnancy test

Boots pregnancy test

Boots does a digital pregnancy test that tells you clearly (using words) if you are pregnant or not. It delivers results in three minutes and is 99% accurate on the day your period is due. It can also be done up to four days in advance but is less sensitive than the more expensive branded products so, when done early, is slightly less likely to give a positive result even if you are pregnant.

However, there is also a Boots Five Days Early pregnancy test which, as the name suggests, can be used five days early for more accurate results. This one's results are displayed using two lines for pregnant and one line for not pregnant.

Tesco pregnancy test Tesco pregnancy test

There's a no-nonsense, at-least-99%-accurate Tesco pregnancy test that gives you a result in one minute. There's also a (more expensive) digital version that uses words to give the result for those who don't like squinting at pink lines.

Superdrug pregnancy test Superdrug pregnancy test

Superdrug has a whole range of pregnancy tests – starting at jaw-droppingly bargainous prices – that are still over 99% accurate, and great for if you want to check, check, and check again. If you're looking for something with more bells and whistles, there's a slightly costlier version that detects pregnancy earlier.

How do you take a pregnancy test?

Most over-the-counter tests contain one or two sticks. You pee on the stick, and the result (positive or negative) appears after several minutes. Read the instructions carefully, because different manufacturers' tests vary slightly, but it usually involves reading one or more lines. If you're feeling particularly flustered, you can always go for the fancypants digital type that says “pregnant” or “not pregnant”, so there's no chance of you misinterpreting the lines.

It used to be that you had to test the urine from your first wee of the day, but now you can use urine collected at any time. If you're doing an early test, however, don't drink tonnes of water beforehand as you don't want your urine to be too diluted.

If you think you might have trouble weeing directly on the stick (and let's face it, we don't all have perfect aim), you can always wee into a clean cup and dip the stick into it for a few seconds.

Where can I get a pregnancy test?

My GP says a line is a line, regardless of the cost of the test – they show the presence of the same hormone. The more expensive tests may just be more sensitive.

Your GP can test to see if you're pregnant, but over-the-counter tests are just as accurate and most surgeries accept these as confirmation that you're on stork watch. You can also get a free pregnancy test from your community sexual health clinic (aka family planning clinics or GUM clinics), NHS walk-in centres and Brook Advisory Centres (if you’re under 25).

Alternatively, get yourself off to a high street chemist or the supermarket, buy a pregnancy test and prepare to join the legions of women who've discovered the profound news that they're going to have a baby while perched on the loo or the side of the bath.

How do pregnancy tests work? Woman is delighted with positive pregnancy result

Pregnancy tests work by detecting the presence of the pregnancy hormone human chorionic gonadotrophin (no wonder they call it hCG) in your urine. The level of hCG goes up steeply during the early weeks of pregnancy. However, some women have low levels of hCG at the time their period would occur so it is possible to get a negative result and still be pregnant.

Different tests have different levels of sensitivity but the packaging will tell you how sensitive yours is. It’s usually described in terms of mIU/ml (milli-international unit per millilitre, or thousands of international units per millimetre). Pregnancy tests generally range in sensitivity from 20mIU/ml to 40mlU/ml. The lower the number, the more sensitive the test is, and, therefore, the earlier it can tell you whether you are pregnant.

Negative pregnancy test results

Getting a negative result can be really disheartening and the stress of trying to conceive can take its toll. If you've been trying for a while and feel you might be having problems getting pregnant it might be worth speaking to your GP about it.

If you get a negative result but you have lots of pregnancy symptoms, such as a missed period or morning sickness and still think you could be pregnant, then wait a couple of days and do another test. NHS Choices says speak to your GP if you get a negative result after the second pregnancy test but your period still hasn't started.

Positive pregnancy test results

If you've got a positive test, I personally wouldn't take any more, otherwise you're just chucking money away to see what you already know in my humble opinion!

If you get a BFP (big fat positive, in Mumsnet-speak), congratulations! Time to crack open the erm, orange juice and get busy with the baby names book! Or you could take the more sensible route and make an appointment to see your GP so that you get your antenatal care started, and start familiarising yourself with the dos and don'ts of pregnancy so you can give your baby the healthiest start possible.

How pregnant am I?

Woman holds a clock

The fancier types of pregnancy test sometimes will say on them that you are “one to two weeks” or “two to three weeks” pregnant if you get a positive result. Don’t forget you need to add two weeks on to this as this represents ‘time since conception’. Midwives (and everyone else) count pregnancy from the first day of your last period, so if you conceived four weeks ago you are six weeks pregnant, and so on.

If you’re still confused, try a pregnancy due date calculator to help give you a clearer idea.

Can the pill give a false positive pregnancy test?

If you haven't come off the pill it makes no odds to the test. Hormone-based contraceptives (the pill, implants and injections) don't affect pregnancy test results. So a positive result means you're pregnant, whether or not you're on the pill.

Remember that a negative result is much more often incorrect than a positive one, though, so if you still think you're pregnant wait a couple of days and repeat the test. If you have an unplanned pregnancy and aren't sure you want to be pregnant you can find lots of women who've been in a similar position on Mumsnet's pregnancy choices Talk board.

My pregnancy test is positive but I'm bleeding. What does this mean?

It's very common to experience bleeding in early pregnancy. It can be a sign that something's amiss, so you do need to see your GP or midwife to check as miscarriage is sadly quite common in the early weeks of pregnancy. However, bleeding and spotting is also common at this time and many women who experience bleeding during early pregnancy go on to have full-term pregnancies, so don't instantly assume the worst.