A home pregnancy test detects the presence of the pregnancy hormone, human chorionic gonadotrophin (hCG), in your urine.  If you test too early, before you’ve even missed a period, there may not be enough hCG in your body for a home pregnancy test to pick up. That’s because levels of the hormone gradually build up as new life begins.  As soon as your egg and a sperm fuse, their genetic material combines to create a new cell. This new cell quickly divides, and each newly created cell divides again and again, growing into the embryo.

Some of the new cells within the embryo will develop into your baby’s placenta. These placenta cells start producing hCG in small amounts even before the embryo implants in your womb (uterus). When the embryo implants, which is when you’re said to have conceived, it produces more hCG. HCG tells your body not to have a period.  The amount of hCG in your bloodstream doubles every two days to three days as the embryo grows and its placenta develops.

Where can I get a pregnancy test kit?

You can buy pregnancy tests, without prescription, online and at pharmacies and supermarkets. You may also be able to get one free of charge from your GP, community contraceptive clinic or local sexual health clinic.

When should I do a pregnancy test?

Hard though it is to wait, it may be less frustrating if you test after you’ve missed a period. Testing too early may not give you an accurate result, although some tests claim to be able to detect pregnancy four days before your period’s due. At this stage, levels of hCG in your system will still be relatively low. So you may end up needing to do another test in a few days’ time to be sure.

Most tests are sensitive enough to detect hCG in your urine from the first day your period is due. At this point you will be about four weeks pregnant.  However, every pregnancy is different, and the rate at which hCG levels increase varies a lot. Sometimes, levels may still not be high enough to detect on the day your period is due.  Levels of hCG peak at about six weeks of pregnancy. So, by the time your period is a week or two weeks late, you should get a definite result.

If you have irregular periods, it may be harder to work out when your next period is due. Allow for your longest cycle in recent months before testing. Alternatively, wait three weeks after you think you may have conceived before doing a test.  If you have recently stopped taking the pill, you may not know how long your natural cycle is. If your test is negative, try testing again in three days’ time.

Depending on the test you’re using, you can test at any time of day. When you decide to test, try not to drink too much beforehand, as it could dilute the levels of hCG in your urine. Some tests may recommend that you use the first urine of the day, particularly when testing early. Levels of hCG become more concentrated in your urine overnight.

How long does it take to get a pregnancy test result?

Check the instructions that come with your test, but you should see the results in about one or two minutes. It can feel like the longest wait ever!

Are home pregnancy tests accurate?

Home pregnancy tests are accurate if you follow the directions to the letter. Having said that, some tests are more sensitive, and easier to use and interpret, than others. The more sensitive a test is, the better it is at picking up low levels of hCG in your system.  If you can’t wait until you’ve missed a period, digital pregnancy tests are reported to be more accurate than non-digital test kits. It’ll still depend on the sensitivity of the kit, though. You can find out how sensitive a home pregnancy test is by reading the information that comes in the test box. You will see that concentrations of hCG are reported in milli-International Units (mIU) per millilitre.

The lower the number, the more sensitive the test. So a test that has a sensitivity of 10mIU/ml is more sensitive than one with a sensitivity of 40mIU/ml. All tests on the market claim to be able to detect a pregnancy with around 99 per cent accuracy if you test on the day your period is due.  However hard it is to wait for that missed period, there’s no substitute for patience. Researchers have questioned the accuracy claims made by some pregnancy test manufacturers, and have called for better product comparisons.

Is it possible to get a false negative?

It is possible. If you test too early, before the first day of your missed period, you may get a false negative result because not enough hCG has built up in your system.  If the test comes back negative but you still suspect you’re pregnant, wait at least three days, and try testing again.

Is it possible to get a false positive?

False positives, when the test says you’re pregnant but you’re not, are rare but not impossible. Some medicines such as fertility drugs, which contain hCG, may affect the test results.  If you’re taking medication – on prescription from your doctor, or bought over the counter – the patient information leaflet that comes with it will tell you if it could affect a pregnancy test result. Check with your doctor or pharmacist if you’re not sure. Sometimes, with non-digital test kits, you may get a faint line that can be difficult to interpret. Find out what this may mean.

How are home pregnancy tests different from tests done by doctors?

Many doctors use the same home pregnancy tests if they need to confirm a pregnancy.  Your doctor may suggest you have a blood test for hCG if you’re showing symptoms of an ectopic pregnancy or a molar pregnancy, or if you’ve had either type of complication before. These need treatment as soon as possible, so the earlier they’re discovered, the better. A blood test is much more sensitive than a urine test. It can tell whether you’re pregnant as soon as six days after fertilisation. This is before an ultrasound scan could pick up a pregnancy. Your doctor will probably refer you to your nearest early pregnancy assessment unit (EPAU) to have your blood test, if you need one.

Original article: https://www.babycentre.co.uk/a2029/home-pregnancy-tests