Double Marker Test

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Studies say that nearly one in twenty pregnancies could have birth defects and these can range in severity from anatomical abnormalities to mental retardation. Some couples have a much greater risk than others to have a child with birth defects based on certain factors. This risk for an inherited condition can be ascertained with the help of genetic screening.  This screening usually done after eight weeks of pregnancy makes use of a number of different diagnostic tests to help identify couples who have an increased risk of age-related or familial genetic disorders and birth defects related to toxic or environmental exposures. Prenatal screening tests are often non-invasive and can be done in a matter of minutes.

A double marker test or a dual marker test is a type of prenatal blood test that is done during the first trimester of pregnancy to check for any abnormalities that might be present in the chromosomal development of the baby. Such anomalies in the chromosomes can lead to severe health conditions and disorders that can affect the baby’s growth within the foetus, or even later in life. The double marker test can help identify in advance about the possibilities of certain disorders like Down’s syndrome or Edward’s syndrome. This test is often suggested as it is a very reliable test that helps detects abnormalities quite accurately.

The factors that are taken into consideration by doctors, before prescribing the double marker test are; if the woman is over 35 years of age, if there is a family history of congenital disabilities and if there is a family history of diabetes. A double marker test is essentially a blood test that doesn’t call for any preparations. Any medical conditions or allergies must be informed to the doctor prior to taking the test. You may be asked to discontinue the use of certain medications before taking the blood test.

The double marker test is performed with an ultrasound and the test results usually fall into two categories: screen positive and screen negative. The results of the test do not merely depend on the blood samples collected but also on the age of the mother and the age of the foetus as observed during the ultrasound. All these factors work together in determining the result. The blood sample is observed to check the levels of the hormone free-beta HCG and pregnancy-associated plasma protein A (PAPP-A). This glycoprotein hormone is developed during the pregnancy by the placenta. The high levels of the free-beta HCG indicate a higher risk of Down’s syndrome and low levels of protein also pose a risk of Down’s syndrome.

The result of the double marker test is presented in the form of ratios. If the ratio is between 1:10 to 1:250, it is termed as a “screen positive” result which lies in the high-risk zone. A ratio of 1:1000 or above is termed as “screen negative” result which shows a low risk. These ratios are pointers for understanding the probability of a child suffering from any disorder. In case the result of the double marker test is positive, the doctor might recommend further diagnostic procedures like amniocentesis or chorionic villus sampling to find the problem.

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