Whether it's expected news or a complete shock, the moment you find out you're pregnant is one you'll never forget. Pregnancy tests, in particular home pregnancy tests, are funny things. They look completely harmless, and there's a rather humorous side to them, too. There's something about going to the store and buying a pregnancy test that makes you feel like a naughty teenager. You wonder who's watching you, and what they think. And then after that, there's the fact you have to have a wee on a stick! But deep down, pregnancy tests are serious business. After all, in just 3 short minutes they have the power to change lives forever.

How They Work

There are two ways to get a confirmation of pregnancy; the urine-based home pregnancy test that can be bought from any drugstore, and the blood test that's usually offered by hospitals health clinics. Both work in the same way; by measuring levels of Human Chorionic Gonadotropin (HCG) in the body.

HCG is a chemical created by the placenta which in turn encourages the production of progesterone which is vital for maintaining healthy, thick and padded uterine walls that protect the fertilized egg. In a healthy pregnancy HCG levels tend to double every 3 days until around 12 weeks gestation. At this point, they decrease gradually until birth.

When To Test

HCG levels can usually be detected through a blood test 11 days after conception, and 14 days after conception by a urine test. However, to ensure more accurate results, many home pregnancy tests recommend you don't test earlier than 21 days after ‘doing the deed', or before the day your period was due. Some brands market super sensitive tests that can be used from 4 days before your period is due, although it's always recommended that you test again a few days later incase HCG levels were too low to be detected that early.


Both blood tests and urine tests are both incredibly accurate; between 97 to 99%. Although not common, false negatives can happen, usually because the test has been taken too early and the HCG levels are not high enough to be detected. There are some other reasons for false negatives, including bad technique (well, it can be difficult to bend that way!) and not waiting long enough before checking the results (it's a nerve wracking time, so you can be forgiven for jumping the gun a little bit!).

False positive are even less common, and if you do get a positive result, chances are you really are pregnant. However, there are a few reasons why a test may show those two little blue lines even when there's no baby on board. Some medications such as anti-anxiety and antipsychotic treatments can interfere with accuracy, as can HCG shots used in some fertility treatments so it's best to wait until all medications are out of your system before testing to avoid any unexpected surprises. Evaporation lines on urine tests are also a sneaky little interference. If a test is left too long, a faint line may appear where the urine has evaporated from the test strip.

If you've recently experienced a chemical pregnancy, a miscarriage, or undergone an abortion, HCG levels may hang around your body for a few weeks before diminishing completely, so in these circumstances a test may provide a false positive.