Malaria Detection PCR Test

Double Marker Test Overview

It is a simple blood test done during first trimester of pregnancy to screen for certain chromosomal anomalies in the fetus. Hence double marker blood test is also called first trimester maternal serum screening test. This test forms a vital component of first trimester screening in pregnancy and should be an integral part of antenatal care of all pregnant women.

It is only a predictive test (not a definitive test) which means this test only tells the likelihood of the fetus having chromosomal anomalies. Hence confirmatory tests are further needed if the result of this test comes as moderate or high risk. The confirmatory tests done are chorionic villous sampling and amniocentesis. The markers tested are free-beta HCG and PAPP-A, hence called double marker test. This test is usually done between 11 weeks -14 weeks of pregnancy.

In a normal pregnancy the fetus has 22 pairs of chromosomes (i.e. 44 autosomal chromosomes and 2 sex chromosomes, XX in female fetus and XY in male fetus).
Chromosomal anomalies can affect any of these chromosomes.

​The various chromosomal anomalies screened by double marker test in pregnancy are:

• Down’s syndrome –in this anomaly there is extra copy of chromosome 21. Therefore it is also called trisomy 21.

• Edward’s syndrome-in this anomaly there is extra copy of chromosome 18. Hence it is also called trisomy 18.

Why is double marker test prescribed?

The health care provider may ask a pregnant woman to undergo this test in first trimester to assess the risk of Down’s syndrome and other chromosomal abnormalities like trisomy 18 in the fetus. This test is not compulsory but is advisable in those pregnant women with risk factors such as:

• Age above 35 years

• Family history of congenital anomalies

• Family history of diabetes

 Components of Double Marker Blood Test

Double marker blood test includes measurement of two biochemical markers in blood:

• Free beta subunit of human chorionic gonadotrophin(free beta-hcg)-its level increase with various chromosomal anomalies such as down’s syndrome

• Pregnancy-associated plasma protein A(PAPP-A)-its level decreases in various chromosomal anomalies 

The result of the double marker test is interpreted as per risk ratios, such as 1:250 or 1:1000, and show the probability of chromosomal abnormalities:

Normal (Low Risk) Results: A low-risk result indicates that there is little chance of genetic abnormalities. A ratio of 1:1000, for instance, indicates that the kid has a 1 in 1000 probability of having the ailment.

High-Risk Abnormal Results: A high-risk result indicates a higher likelihood of chromosomal abnormalities. For instance, additional diagnostic testing could be necessary to validate the results if the ratio is 1:250 or less.

Procedure and prerequisites

The procedure of double marker test is simple. The clinician would withdraw some blood and take it for the testing. You may feel some pain due to needle prick. No special preparation is needed for this test.

A maternal screen consent form needs to be filled with few other details along with the latest ultrasound scan report (First trimester scan) copy.