Pregnancy test

Pregnancy test
Medical diagnostics
A modern pregnancy test
MeSH	D011258
MedlinePlus	003432
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A pregnancy test attempts to determine whether a woman is pregnant. Markers that indicate pregnancy 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 cannot be detected until after implantation: this results in false negatives if the test is performed during the very early stages of pregnancy. 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.

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 hCG, or human chorionic gonadotropin, 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.