<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> <P> The test for pregnancy which can give the quickest result after fertilisation is a rosette inhibition assay for early pregnancy factor (EPF). EPF can be detected in blood within 48 hours of fertilization . However, testing for EPF is expensive and time - consuming . </P> <P> Most chemical tests for pregnancy look for the presence of the beta subunit of human chorionic gonadotropin (hCG) in the blood or urine . hCG can be detected in urine or blood after implantation, which occurs six to twelve days after fertilization . Quantitative blood (serum beta) tests can detect hCG levels as low as 1 mIU / mL, while urine test strips have published detection thresholds of 10 mIU / mL to 100 mIU / mL, depending on the brand . Qualitative blood tests generally have a threshold of 25 mIU / mL, and so are less sensitive than some available home pregnancy tests . Most home pregnancy tests are based on lateral - flow technology . </P> <P> With obstetric ultrasonography the gestational sac sometimes can be visualized as early as four and a half weeks of gestation (approximately two and a half weeks after ovulation) and the yolk sac at about five weeks' gestation . The embryo can be observed and measured by about five and a half weeks . The heartbeat may be seen as early as six weeks, and is usually visible by seven weeks' gestation . </P>

What is the amount of hcg that pregnancy tests detect
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