Pap Smears/Pregnancy Test
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).
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.
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
At the beginning of the 1930s, Hillel Shapiro and Harry Zwarenstein, who were researchers at the University of Cape Town, discovered that if urine from a pregnant female was injected into the South African Xenopus toad and the toad ovulated, this indicated that the woman was pregnant. This test was used throughout the world from the1930s to 1960s, with Xenopus toads being exported live in great numbers.
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.
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.
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.