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What is Triple Marker test?

A triple marker test is a blood test carried out during pregnancy to check for the levels of three substances in a pregnant woman’s blood, human chorionic gonadotropin (hCG), alfa-fetoprotein (AFP) and estriol (a type of estrogen).

Alfa-fetoprotein is a protein produced by the growing foetus. As the foetus develops, the levels of AFP increase gradually and reach a peak value during the second trimester of pregnancy. At this time, AFP becomes detectable in mother’s blood.

Human chorionic gonadotropin is a proteinaceous hormone produced by a woman’s body after the baby is conceived. Its primary function is to support pregnancy. Levels of hCG increase steadily during the time of pregnancy and can be detected in blood. It is not synthesized at any other time in the body.

Estriol is one of the estrogens and a primary female sex hormone. It is required to maintain the menstrual cycle and female secondary sexual characteristics and aids in maintaining pregnancy. A woman’s body produces estrogen at all times in varying quantities; however, its levels increase during pregnancy. Some estrogen is also known to be produced by the foetus.

The changing levels of these three substances in blood can be correlated with some congenital (present from birth) disabilities or birth defects in the growing foetus.

Triple marker test is essentially a just a screening test, which means abnormal levels of these substances do not diagnose a congenital disability but give the doctors enough information to be able to order more specific tests that will lead to a diagnosis.

  1. Why is Triple Marker test performed?
  2. How do you prepare for Triple Marker test?
  3. How is Triple Marker test performed?
  4. What do Triple Marker test results mean?
  5. How much does a Triple Marker test cost?

Triple marker test is performed during the second trimester of pregnancy, specifically during the 16th-18th weeks. This test is advised to all pregnant women to assess the risk of congenital disabilities in the growing baby, but it is specifically recommended under the following conditions:

  • Maternal age of more than 35 years
  • Family history of congenital disabilities
  • Exposure to harmful radiation
  • Use of certain medicines during pregnancy that could affect the foetus
  • If the pregnant woman has diabetes
  • If the woman acquires a viral infection during pregnancy

Triple screening is a useful test to get to know the risks associated with the continuation of that pregnancy. Certain disorders that are screened with this test are:

  • Down syndrome
  • Edwards syndrome
  • Neural tube defects (defects of the brain, spine or spinal cord)
  • Other chromosomal abnormalities

Sometimes, the test can also prove to be useful in detecting multiple pregnancies and understanding the progress of pregnancy.

The test does not require much preparation beforehand. However, for the ease of diagnosis, it is important for the woman to inform the doctor about the medicines she may be taking and give a detailed medical history.

Triple marker test can be performed at any time during the day and will only take a few minutes. A technician will clean an area on your upper arm with an antiseptic solution and tie a tourniquet to help locate a vein easily. Using a sterile needle, he/she will withdraw a small amount of blood. This might cause slight discomfort or pain. The blood sample will be deposited in a vial, and the site of the puncture will be covered with cotton gauze and bandage. Some women may develop a bruise at the site of puncture, but it will fade away soon.

Normal results:

Normal values of the triple markers, when measured around the 16th week, are:

  • AFP: 10 to 150 ng/mL
  • hCG: 9,000 to 210,000 U/L
  • Estriol: 4 nmol/L

Abnormal results:

Abnormal results are sometimes called a "positive" result, which means the foetus may be at risk of developing a congenital disability. The following list correlates the change in values of the three marker tests with the possible underlying conditions:

  • A higher than normal value of AFP is associated with neural tube defects like spina bifida and anencephaly. A lower than normal value is associated with Down syndrome.
  • Higher than normal hCG values can be associated with Down syndrome. Lower than the typical values of hCG could be an indication of a risk to the pregnancy itself.
  • Decreased values of estriol are also an indication of Down syndrome.

The test is known for a high percentage of false positives, which means even if there is no risk of congenital disabilities, the test may indicate it so. Therefore, it is essential to remember that the triple marker test is only a screening test that allows the doctors to order for further tests that will help determine the underlying condition if any.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.  

The cost of the triple marker test may range from 1,200 to 2,600 INR based on the city and laboratory in which the test is conducted.

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References

  1. American Pregnancy Association: Triple Screen Test
  2. Gerard J. Tortora, Bryan Derrickson. Principles of anatomy and physiology. 14th ed. Wiley Publication; 2014. Chapter 29, Development and inheritance; p.1096-1111.
  3. Marshal W.J, Lapsley M, Day A.P, Ayling R.M. Clinical biochemistry: Metabolic and clinical aspects. 3rd ed. Churchill Livingstone: Elsevier; 2014. Chapter 22, Reproductive function in the female; p.436-437.
  4. Gerard J. Tortora, Bryan Derrickson. Principles of anatomy and physiology. 14th ed. Wiley Publication; 2014. Chapter 29, The reproductive system; p.1070-1072.
  5. American Academy of Family Physicians [Internet]. Leawood (KS); Triple Screening in Pregnancy—What It Is and What to Expect
  6. Adigun OO, Khetarpal S. Alpha Fetoprotein (AFP, Maternal Serum Alpha Fetoprotein, MSAFP) [Updated 2019 Feb 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019
  7. Health direct [internet]: Department of Health: Australian government; hCG levels
  8. Training Courses: Geneva Foundation for Medical Education and Research; Second Trimester Maternal Serum Screening Programmes for the Detection of Down's Syndrome