<P> Hormonal pregnancy tests such as Primodos and Duogynon were used in the 1960s and 1970s in the UK and Germany . These tests involved taking a dosed amount of hormones, and observing the response a few days later . A pregnant woman does not react, as she is producing the hormones in pregnancy; a woman not pregnant responds to the absence of the hormone by beginning a new menstrual cycle . While the test was (is) generally considered accurate, research advancements have replaced it with simpler techniques . </P> <P> Immunologic pregnancy tests were introduced in 1960 when Wide and Gemzell presented a test based on in - vitro hemagglutination inhibition . This was a first step away from in - vivo pregnancy testing and initiated a series of improvements in pregnancy testing leading to the contemporary at - home testing . Direct measurement of antigens, such as hCG, was made possible after the invention of the radioimmunoassay in 1959 . Radioimmunoassays require sophisticated apparatus and special radiation precautions and are expensive . </P> <P> Organon International obtained the first patent on a home pregnancy test in 1969, two years after product designer Margaret Crane noticed that the laboratory testing procedure was relatively simple and made a prototype . The product became available in Canada in 1971, and the United States in 1977, after delays caused by concerns over sexual morality and the ability of women to perform test and cope with the results without a doctor . </P> <P> Another home pregnancy testing kit was based on the work of Judith Vaitukaitis and Glenn Braunstein, who developed a sensitive hCG assay at the National Institutes of Health . That test went onto the market in 1978 . In the 1970s, the discovery of monoclonal antibodies led to the development of the relatively simple and cheap immunoassays, such as agglutination - inhibition - based assays and sandwich ELISA, used in modern home pregnancy tests . </P>

When did pregnancy tests over the counter became available