<Tr> <Th> MedlinePlus </Th> <Td> 003432 </Td> </Tr> <P> A pregnancy test attempts to determine whether or not a woman is pregnant . Indicative markers are found in blood and urine, and pregnancy tests require sampling one of these substances . The first of these markers to be discovered, human chorionic gonadotropin (hCG), was discovered in 1930 to be produced by the syncytiotrophoblast cells of the fertilised ova (eggs). </P> <P> While hCG is a reliable marker of pregnancy, it cannot be detected until after implantation; this results in false negatives if the test is performed during the very early stages of pregnancy . HCG can be detected via blood 8 days after fertilization of the egg, and in the urine 10 . </P> <P> Obstetric ultrasonography may also be used to detect pregnancy . Obstetric ultrasonography was first practiced in the 1960s; the first home test kit for hCG was invented in 1968 . The kits went on the market in the United States and Europe in the mid-1970s . </P>

When does pregnancy test become positive after implantation