You might be able to acquire a positive pregnancy test by the end of this week. Pregnancy tests detect the presence of a hormone known as human chorionic gonadotropin (hCG) in your urine. HCG is only produced by pregnant women, so if you get a positive result, you have found evidence that you are indeed pregnant. Since the early days of pregnancy, a growing embryo/fetus produces hCG, which allows for it to be detected by a blood test or urine test. As the level of hCG increases so does the reliability of the test. Most commercial pregnancy tests work on this principle. They contain antibodies that bind to hCG, which can then be detected by a color change or fluorescence when exposed to a solution containing the antibody. As the levels of hCG increase so does the sensitivity of the test. This means that it will give a positive result for pregnancies as early as 7-10 days after conception. This is why it is recommended to wait at least until the first trimester before having a pregnancy test performed. A negative test does not guarantee that you are not pregnant. It may just mean that the hCG was released from tissues elsewhere in your body, not necessarily from the developing fetus. A second consecutive negative test reduces the chance of this happening further and confirms that you are not pregnant.