Pregnancy Test
Pregnancy tests are designed to determine if your urine or blood contains a hormone called human chorionic gonadotropin (hCG) whose in-body level is closed related with pregnancy. HCG is produced right after a fertilized egg attaches to the wall of a woman's uterus.
This usually happens, but not always, about six days after fertilization. If you're pregnant, levels of hCG continue to rise rapidly, doubling every two to three days.
Pregnancy Test Principle
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.
Pregnancy Test Types
Two types of pregnancy test available: urine tests and blood tests.
Urine pregnancy tests can be done at home or in a doctor's office. Many women first choose a home pregnancy test to take about a week after a missed period. Home pregnancy tests are private and convenient.
These products come with instructions. Follow them closely for the most accurate results. After testing, you can confirm results by seeing your doctor, who can perform even more sensitive pregnancy tests.
Blood pregnancy tests are done at your doctor's office, but are used less often than urine tests. These tests can detect pregnancy earlier than a home pregnancy test, or about six to eight days after ovulation. But with these tests, it takes longer to get the results than with a home pregnancy test.
Two subtypes of blood pregnancy tests: qualitative hCG test and quantitative hCG test.
Pregnancy Test, application of ELISA assay
In home pregnancy test, direct measurement of antigens, such as human chorionic gonadotropin (hCG). Radioimmunoassays require sophisticated apparatus and special radiation precautions and are expensive. 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 that are used in modern home pregnancy tests.
Home pregnancy test utilizes the principle of sandwich enzyme immunoassay, with a unique mono-mono antibody combination specific against hCG present in urine/serum. The patient's urine/serum specimen is allowed to react with the monoclonal antibody directed against hCG, coated on the microtiter wells and the monoclonal antibody - enzyme conjugate complex. If hCG is present in the test specimen, antibody-hCG-antibody enzyme complex will be formed on the surface of the microtiter well. Washing the well under running tap water will clear off the unbound complex and the unreacted conjugate. Incubating the well with substrate reagent results in the development of blue colour. The intensity of the blue colour is proportional to the concentration of hCG present in the urine/serum specimen. Visual comparison of the intensity of blue colour with test specimen well as against the positive control well indicates the concentration of hCG greater than or equal to 25 mIU/ml of hCG in the test specimen.
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