A urine pregnancy test measures the amount of human chorionic gonadotropin (hCG) in the urine. hCG is a hormone found only in a pregnant woman. Home pregnancy tests are urine pregnancy tests and are a popular way to detect pregnancy. There is a wide variety of tests available in the market today and are a convenient way to find out if one is pregnant.
However these tests only detect the amount of hCG when it reaches a certain level. Some tests may be more sensitive than others and may be able to detect low levels of hCG even a few days before your period is due.
hCG is secreted after implantation by those cells which go on to form the placenta. It is best to take a home pregnancy test (HPT) about a week after you miss your period. Taking the test early on in pregnancy can result in a false negative result. Almost all urine tests will give you a proper reading if you test about two weeks after you ovulate. The best time to take the test is first thing in the morning as the hCG samples are most concentrated at this time. The test can be performed within five minutes or so and only one or two drops of urine are required. You will either have to pass urine directly onto the chemically treated strip or use a dropper to place the urine sample on the stick. If the pink or blue lines on the strip change color, the test is positive. Some tests have a symbol on them which denotes pregnancy. Most tests have a control indicator (a second line) which indicates whether the test is valid.
Most urine pregnancy tests are about 99% accurate. There have been cases of a false negative result i.e. when you are pregnant but the test says you are not. Reasons for this include taking the test too early or not following the instructions completely. This also includes a missed reaction time -not waiting for the time mentioned in the instructions to lapse before reading the test. hCG levels develop at different rates for different women and it could be that the test is not sensitive enough to read the level. Occasionally an ectopic pregnancy or a problematic pregnancy might cause low hCG levels which the test does not react to. Diluted urine could be another reason for inaccuracy. Prescribed medication could also affect the results.