All About Pregnancy Tests

Are you curious about pregnancy tests and how they work? Whether you’re trying to conceive or just want to be prepared, understanding pregnancy tests is an important part of your journey to motherhood. In this article, you’ll get all the information you need to know about pregnancy tests, including when to take one, how accurate they are, and what to expect when you take the test. So, if you’re looking for insight into pregnancy tests, you’ve come to the right place!

How Do Pregnancy Tests Work?

Pregnancy tests work by detecting a pregnancy hormone called hCG, (human chorionic gonadotropin), in either your urine or blood. This hormone is produced from about six days after conception. During early pregnancy hCG levels double every two days, so hCG becomes easier to detect on a test as the days progress. This is why it's a good idea to wait until after the first day of your missed period to take the pregnancy test, as taking the test any earlier may result in a false negative.


What Types of Pregnancy Tests Are There?

To detect the presence of hCG, you can use two different types of pregnancy tests: urine tests and blood tests.

A Urine Pregnancy Test

Home pregnancy tests work by detecting hCG in your urine. You'll find a range of brands available on the market including some digital pregnancy tests. Some brands are more sensitive than others – meaning they may even work four or five days before your period is due. These tests allow you to check for pregnancy in the privacy of your own home at a time that suits you. If you'd like help taking the test, you can ask your GP or the staff at your local sexual health clinic. The process for taking a home pregnancy test is relatively straightforward; here’s what to do:

  1. Read the instructions. Make sure to carefully follow the instructions inside or on the pack. Each brand is a little different, for example, you may have to wait until at least the first day of your missed period for some tests to be accurate.

  2. Remove the stick (and cup) from the packaging. What does a pregnancy test look like? You may need to pee on a test stick by holding it under your urine stream for a few seconds, while other tests require you to pee into a cup and then place the stick into the urine for a time.

  3. Pee. Depending on the instructions, you’ll pee directly on the stick – a prepared chemical strip – or dip it into a urine cup.

  4. Wait. The results usually appear within a few minutes but keep in mind the wait times can be a little different among brands so follow the instructions. Don't check the result too early otherwise you may not get an accurate reading, and in some cases, you shouldn't read the result after about 10 minutes as it may no longer show the accurate result. Sometimes, an evaporation line may appear on a pregnancy test if you leave it to sit for too long. You may even want to set a timer, so you check the test results within the brand's recommended window.

  5. Read the results. The instructions will tell you how your product will show its results. For example, some pregnancy tests show a positive result by displaying two lines – not just one. In this case, even two faint lines on a pregnancy test may still indicate a positive result and show that you’re pregnant. Other brands show their results in other ways.

If you're in any doubt about your result take the test again in a few days or ask your GP for help.


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A Pregnancy Blood Test

This type of test must be done at the doctor's office, and results may only come back in a few days. Pregnancy blood tests are more sensitive than urine tests and can detect the amount of hCG in your blood – not just whether the hormone is present at all. They can also detect hCG a little earlier – even six to eight days after ovulation. Experts usually recommend taking a home pregnancy test instead of going for the blood test but check with your GP if you're unsure about what's right for your situation.

Where Can I Get a Pregnancy Test?

You can buy a home pregnancy test at many pharmacies and supermarkets. However, you may also be able to get a free test from your GP, at community sexual health clinics, at some youth service centres, and Brook centres if you're 25 or under. All of these services are confidential. Find your nearest pregnancy testing service here.

How Accurate Are Pregnancy Tests?

A positive result on a pregnancy test is almost certainly accurate as long as you have followed the instructions on the pack carefully. However, false positives can happen in rare circumstances, for example, if a pregnancy test picks up on hCG that's been part of your fertility treatment.

A negative pregnancy test result may be less reliable. If have received a negative result but still think you may be pregnant, for example, if your period is late, wait a few days and take another pregnancy test or ask your GP for a pregnancy blood test. These factors may lead to an inaccurate result:

  • Taking the test too early. If you take the pregnancy test before the first day of your missed period, levels of hCG may still be too low for the test to detect this early.

  • Not following the instructions. Check when and how the pregnancy test should be taken and follow these instructions carefully. For example, wait the correct amount of time to read the result.

  • Your fluid intake. This can dilute the amount of hCG in your urine so the test may not be able to detect its presence. It may help to take the test first thing in the morning when levels of hCG are most concentrated in the urine.

  • Taking certain medications. Most medications won't affect a home pregnancy test, but some medications used to treat infertility, and some anticonvulsants, diuretics, sleeping tablets, and others may affect the accuracy of the results. Ask your GP or the pharmacist, or read the instruction leaflet to check for any medicines you're taking.

When to Take a Pregnancy Test?

If you suspect you’re pregnant, you may want to take a pregnancy test as soon as possible, and it’s common to wonder ‘How early can you take a pregnancy test?’ and ‘When’s the best time to take a pregnancy test?’ As we mentioned above, the most accurate time to take a home pregnancy test is from the first day of your missed period onward; however, there are some tests that may be sensitive enough to use before your missed period (but you should check the test instructions carefully).

Waiting until after your first missed period ensures that your levels of hCG are high enough to detect – remember, hCG levels increase as your pregnancy progresses. Your body only produces hCG after the fertilised egg implants itself into the lining of your uterus – this may also cause some implantation bleeding – an early sign of pregnancy, along with missed periods. Your missed period is likely the earliest and most reliable clue that you are pregnant.

You may also be wondering ‘How soon after unprotected sex can I test for pregnancy’? It’s recommended to test at least 21 days after having unprotected sex.

Some other early signs of pregnancy that you may notice include:

  • tender or swollen breasts

  • needing to pee more often

  • feeling nauseous

  • feeling tired.

What to Do After a Positive Pregnancy Test

Once you learn the good news, make an appointment with your GP or midwife so that your antenatal care can start. Congratulations! We're really excited for you.

If you want to know how far along you are, check out our Due Date Calculator to get an approximate idea.


Pregnancy tests detect your body’s hCG levels, which double every two to three days during those first few weeks of pregnancy. To help avoid a false negative, it’s best to wait until after your first missed period to take a pregnancy test.

The Bottom Line

If you've been attempting to conceive, have missed your period, or noticed some of the usual early signs of pregnancy, you may well want to know if you’re pregnant. Home pregnancy tests, which work by detecting levels of hCG in your urine, are an excellent way of confirming pregnancy. For the most precise results, it’s best to wait until after your first missed period and follow the pregnancy test instructions carefully.

There is a whole lot of interesting science that goes into pregnancy tests, but we hope this straightforward guide helps you understand how at-home urine tests work, when to take one and how accurate they are.

You might also want to take a look at our go-to pregnancy guide for interesting and exciting information about what's to come, and you can also sign up for our emails for great tips and articles delivered straight to your inbox.

How We Wrote This Article The information in this article is based on the expert advice found in trusted medical and government sources, such as the National Health Service (NHS). You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.

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