Maternal Triple Marker Test (14 To 20 Weeks)

Triple marker test

It is a simple blood test done during second trimester of pregnancy to screen for certain chromosomal anomalies in foetus. Hence maternal triple marker test is also called second trimester maternal serum screening test. This test forms a vital component of second trimester screening in pregnancy. This screening test 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 foetus having chromosomal anomalies. Hence confirmatory tests   such as amniocentesis are further needed if the result of this test comes as increased risk. The three markers tested are alpha fetoprotein, beta-hCG and unconjugated estriol hence called triple marker test. These three markers are independent predictors of genetic risk and in combination with maternal age generate patient specific risk of a foetus with trisomy21or downs syndrome. Triple test in pregnancy is performed between 15 and 21 weeks of pregnancy.  

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

The various anomalies screened by maternal triple 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.

• Neural tube defects-such as spina bifida and anencephaly.

Why is triple marker test prescribed?​

The health care provider may ask a pregnant woman to undergo triple marker test in second trimester of pregnancy to assess the risk of Down’s syndrome, Neural tube defects and other chromosomal abnormalities like trisomy 18 in the foetus. 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/personal history of diabetes

• Antenatal drug usage with proven  side effects

• Antenatal viral infection

• over exposure to radiation during early pregnancy

What are the components of maternal triple marker test?

Triple marker blood test includes measurement of three biochemical markers in blood:

• Beta subunit of human chorionic gonadotrophin(beta-hCG)-its level increase with various chromosomal anomalies such as Down’s syndrome

• Alpha fetoprotein-it is a protein secreted by liver and gastrointestinal tract of foetus. Its level is low in chromosomal anomalies. Its level increases in neural tube defects.

• Unconjugated estriol-it is a steroid molecule formed from combined activity of foetal adrenal gland and placenta. Its level is low in chromosomal anomalies.

This test is usually done following a second trimester ultrasound examination to assess the risk for above anomalies in the foetus. Few other demographic details are required to calculate the risk, like maternal weight, Date of Birth, diabetes status, smoker or not etc. The result is either screen positive (high risk) or screen negative (low risk).

Procedure and prerequisite

The sample for triple marker test in pregnancy is taken from blood (serum) by inserting a small needle into vein of your arm .A small amount of blood is then collected in test tubeor vial .You may feel some pain due to needle prick. No special preparations are needed for this test.

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