The Pregnancy Test works by measuring the level of the hormone, beta human chorionic gonadotrophin (B-hCG) in your urine (pee). This hormone increases when you are pregnant. Pregnancy tests that you can buy over the counter are just as reliable as the ones that your doctor uses. Usually, you do the test from the first day of your missed period which is usually about two weeks after the egg and sperm have got together. If you think that you might be pregnant but the test is negative, try repeating it one week later, as the test can, first time around, occasionally be falsely negative. On the other hand - if it is positive - it really is positive! You can buy a pregnancy test at the chemist, or you can get a free one at your doctor's surgery, young people's or family planning clinic. The earlier that you know that you are pregnant the better, as if you want to carry on with your pregnancy you will need a check up, and if you don't want to have a baby the earlier you have an abortion the safer it is.