<P> A pregnancy test attempts to determine whether a woman is pregnant . Markers that indicate are found in urine and blood , 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 ) . While hCG is a reliable marker of pregnancy , it can not 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 days after . 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>
<P> A pregnancy test attempts to determine whether a woman is pregnant . Markers that indicate are found in urine and blood , 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 ) . While hCG is a reliable marker of pregnancy , it can not 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 days after . 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 did over the counter pregnancy tests become available
when did over the counter pregnancy tests become available
mid-1970s
mid-1970s