June 17, 2011

Pregnancy Test

pregnancy testPregnancy tests are formulated to confirm that whether a lady is pregnant or otherwise. Tests for pregnancy have been in practice since early human civilizations. Previously pregnancy tests were mostly depending upon the different signs of pregnancy. But the modern pregnancy tests are based upon different chemical markers that start rising up when a lady is pregnant. These pregnancy markers can be found both in blood and urine. But due to patient’s convenience, modern pregnancy kit tests use urine as a sample.

The most common sought after chemical marker in pregnancy is Human Chorionic Gonadotropin. It is secreted by the HCG producing cells present in the placental wall. Although detecting HCG in urine is a confirmatory test for pregnancy, the level of HCG can raise in some rare tumors of the ovary, chronic diseases of liver, cancer of the liver and in some other disease conditions. In a pregnant woman, the level of HCG initially rises slowly and the pregnancy tests will give positive results only after 6 days of conception. Otherwise there is a fair chance of detecting a false negative case. False positive result can be seen in a lady taking HCG injections for infertility or for any other reason. Modern test kit is supplied with a paper strip impregnated with a chemical solution for detecting HCG. The kit also has a place to pour some urine sample. Usually the first morning sample is preferred. Positive test will show two bands in the examination area. And if the urine does not contain HCG, then there will be only one control band. The test will not take more than a few minutes and it is highly accurate (gives confirmatory result in 99% of cases). It is better to take less amount of water at night prior to the test, so the concentration of HCG will be higher in morning urine.
In the laboratory, urine sample is analyzed for presence of HCG. The test is called Beta-Gravindex tests. Although the technique is mostly similar, the test at the laboratory is done with some machines.
Blood samples are also analyzed in the laboratory to quantify the amount of HCG present in the sample. This is called Beta-HCG test. As little amount of HCG can also be demonstrated by this method (1mIU/ml), Beta-HCG test can give positive result as early as 6 days after conception.

For all practical purposes, detection of planned pregnancy can wait up to seven days of a missed conception. But academically pregnancy test can give positive results even after 48 hours of fertilization. The chemical marker for this test is called Early Pregnancy Factor (EPF). A test called RIA (Rosette Inhibition Assay) is done to detect the EPF. Although the test is very much accurate (99.5%), it takes about 3-4 hours for a single test and it is quite expensive. Therefore, use of this test is limited to some unprecedented conditions like sexual assault and when the victim feels that she can become pregnant (depending the date of menstruation).
Visualizing the uterus for presence of fetal sac by Ultrasonography (USG) can be done 2 weeks after conception using a transvaginal probe. After 5 weeks the fetus is visualized and the fetal measurements can be obtained. Fetal heart beat can be measured by USG only after 7 weeks of gestation.

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