After pregnancy occurs, the developing placenta begins producing a hormone called human chorionic gonadotropin. The level of this hormone rapidly builds up in the body, according the University of Maryland Medical Center. Home pregnancy tests work by measuring the amount of human chorionic gonadotropin in urine. A home pregnancy test that yields a positive almost always means there is a pregnancy. A negative result does not always mean that there is not a pregnancy because the level of hormone may not have built up to a detectable level yet. There are two basic types of home pregnancy tests.
Urine Stream
These home pregnancy tests work by placing a test strip or a dipstick type of device into the urine stream. The test strip or dipstick can also be placed into a sample of urine, such as urine that is in a cup. If the test strip or dipstick in placed into a sample of urine, there is typically a window of time for the placement into the sample to ensure accuracy. At the end of the dipstick or test strip, there is an area that will change color if there is human chorionic gonadotropin present. A change in color indicates pregnancy.
Collection Cup
These home pregnancy tests work by collecting urine in a collection cup. There are two types of testing methods in this category. In one type, drops of urine are then placed into the well of a test device. An area of the test device will change color if human chorionic gonadotropin is present, indicating pregnancy. With the other type of collection cup home pregnancy tests, the test device is placed into the collection cup. An area of the test device will change color in the presence of human chorionic gonadotropin, indicating pregnancy.
Other Factors
Regardless of the type of home pregnancy test used, the urine collected after first waking up in the morning will produce results that are more accurate than urine collected later in the day. The sensitivity of home pregnancy tests varies. The more sensitive the test is to human chorionic gonadotropin, the earlier it can detect pregnancy.
