The presence of human chorionic gonadotropin (hCG) in a urine sample is detected by home pregnancy tests. A false negative reading can be caused by a number of factors, including incorrect use of the test, testing too soon, using an outdated test, or diluting the urine by drinking too much water beforehand. A positive result may indicate a problem with your reproductive system, such as polycystic ovary syndrome (PCOS). A negative result does not guarantee that you are not pregnant. It only means that there was no hCG present in the urine sample taken at the time of the test. Home pregnancy tests work on the principle of hCG being released from the placenta into the blood stream during pregnancy. The test detects the presence of this hormone in the urine and provides a reading either visually or via a line of beads that changes color when there is a change in pH. These tests require a single morning urine sample. If you are unable to provide a suitable sample, repeat the test later in the day. It is important to remember that a negative result does not guarantee that you are not pregnant. A woman's body produces some hCG even after she has had children, so a second child might still show up as a positive result on a home pregnancy test. Women who have irregular periods or who use hormonal contraception or IUDs/IUSs should wait at least three months after stopping contraception before having their fertility tested with a home pregnancy test.