How a Pregnancy Test Kit Works? Detection of hCG: Pregnancy test kits work by detecting the presence of the hormone human chorionic gonadotropin (hCG) in a woman's urine. This hormone is produced by the placenta shortly after the embryo attaches to the uterine lining. Sample Collection: A small amount of urine is collected, usually by either holding the test strip in the urine stream or dipping it into a cup of collected urine. Reaction Strip: The test strip contains antibodies that are sensitiv