Written By: Debjani Arora | Updated : July 28, 2016 9:25 AM IST
There are various tests done during pregnancy to check maternal and foetal wellbeing. Marker tests are usually done to check for congenital and genetic defects in the foetus. Often they are done to check if the foetus is suffering from Down s syndrome, a chromosomal abnormality which affects both the physiological and psychological development of the child. This is the reason why screening tests are taken more seriously during the first and second trimester. Here Dr Meghana Sarvaiya, Consultant Gynaecologist and obstetrician, Cloudnine Hospital, Mumbai, tells you the importance of these screening tests.
Dual marker test
This is a screening or a blood test done during the first trimester between the 11th and 13th week of your pregnancy. A dual marker test is done along with a Nuchal translucency scan or NT scan. The blood test measures two markers namely hCG (human chorionic gonadotrophin), and PAPP-A (pregnancy-associated plasma protein) whereas the NT scan measures the fluid under the skin at the back of the baby s neck. The scores of both these tests are considered to check if a child suffers from Down s syndrome. In case, of a risk of Down s syndrome, the reports would show abnormal levels of hCG and PAPP-A and a higher NT scan value. Depending on the results, the expectant mother either falls in screen positive or high risk or screen negative or low risk category. In India, the chance of a mother carrying a Down s syndrome baby is 1 in 350. If the risk is less, the mother falls in screen negative category. Depending on the result, the expectant mother will be advised to go for a more invasive test like amniocentesis or CVS sampling.
Triple and quadruple marker test
A triple or a quadruple marker test is done during the second trimester of pregnancy, ideally during the 15th to 20th week. A quadruple marker is more sensitive than a triple marker test and a mother is usually asked to go for the same to ascertain genetic defects in the foetus. In a quadruple marker, four markers in the blood are measured, namely b-hCG (beta subunit of human chorionic gonadotrophin), AFP (serum alpha-fetoprotein), uEst (unconjugated estriol) and Inhibin A. In case, you have a risk of carrying a Down s syndrome baby, the levels of hCG would be high while AFP and uEst would be low. Depending on the results, the mother will be put in high or low-risk category. Doctors will then suggest other invasive tests.
P.S.: All these screening tests have an accuracy of 99.9 percent. Any major decisions taken should be done after detailed consultation with the doctor.
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