- What is a double marker test?
- Why is the double marker test done?
- Do you need to prepare for the test?
- How is the double marker test done?
- What if the test results are not within the normal range?
- Advantages of a double marker test
- Drawbacks of the double marker test
- What is the cost of the test?
Double marker test is a prenatal test performed as a screening tool to predict the possibility of chromosomal abnormalities, especially the Downs Syndrome in the baby. This test has become available in the recent years as a result of analysis of massive data retrieved and studied. To learn about why, when and how this test is performed, read this MomJunction post.
What Is The Double Marker Test?
A double marker (dual marker) test is a non-invasive screening done during the first-trimester to detect aneuploidy (presence of abnormal chromosome number) pregnancies. It plays a prominent role in identifying the likeliness of having a baby with neurological conditions, such as Down’s syndrome (trisomy 21), Edward’s syndrome (trisomy 18), and Patau’s syndrome (trisomy 13). It is usually done between the 10th and 14th weeks of pregnancy (1).
Why Is The Double Marker Test Done?
Pregnant women who fall under a particular risk category may have to undergo this double marker test in their first trimester. The risk factors include:
- Age above 35 years
- Previous baby born with any chromosomal abnormality
- A family history of genetic conditions
- IVF pregnancy
- History of insulin-dependent type-1 diabetes
- History of consumption of medications such as antiepileptic medications and exposure to high-grade fever
- It is offered to all pregnancy moms universally but is not a mandatory test
Do You Need To Prepare For The Test?
The double marker test does not need any specific preparations. Let your doctor know if you are on any medications since you might be advised to refrain from them for sometime before the test.
How Is The Double Marker Test Done?
The dual marker test analyses two markers in the mother’s blood and therefore is named so. It is correctly called as the Combined Test as it combines the Nuchal Translucency (NT) scan with these two markers that measure the fluid behind the fetal neck to screen for Down syndrome
The two markers are:
- Free beta hCG (human chorionic gonadotrophin): High levels show the risk of Down’s syndrome, and low levels indicate Edward’s syndrome.
- PAPP-A (Pregnancy-associated plasma protein): Low levels show the risk of Down’s syndrome (2).
- The result comes as low, moderate or high probability of having the disorders.
- When the result is “low”, it means that there is 98 to 99 % possibility that the disorder is absent.
- When the results are “moderate to high”, it needs further confirmation by amniocentesis (study of cells of the baby retrieved from the fluid around the baby). Amniocentesis is invasive as it entails accessing this fluid through a needle introduced in the mother’s womb, and is associated with possibility of misscarriage.
Presently, NIPT (Non Invasive Perinatal Testing) has become available with a comparable sensitivity to amniocentesis. In this test, the mother’s blood is collected and cell free DNA of the baby is studied (3) (4).
What If The Test Results Are Not Within The Normal Range?
If the beta hCG levels are more than the normal range, it is a positive marker for Down syndrome. If coupled with low PAPP-A value, it is taken as a positive double marker, and you may need additional tests to confirm the diagnosis.
Further tests would be invasive, such as amniocentesis and chorionic villus sampling (CVS), and would test the fetal cells present in the amniotic fluid (5).
Advantages Of The Double Marker Test
- It offers enough time to decide on additional tests if they detect a chromosomal abnormality in the fetus.
- The results are reasonably accurate.
- You can go for early termination that holds fewer complications.
- Additionally, it can help to tag pregnancies which can land in pre-eclampsia, placental separation, and fetal growth restriction. Thus offering an early opportunity to modify these conditions.
Drawbacks Of The Double Marker Test
- It is expensive.
What Is The Cost Of The Test?
The cost of the double marker test varies across cities and hospitals. It might range from INR2,500 or more based on location, quality, and availability.
Every pregnancy screening test has its significance. However, you should be discussing all the pros and cons with your doctor before going for any test. If the results are positive, wait for your doctor’s confirmation before worrying. The test is a useful tool to help identify abnormalities in the baby and adverse outcomes in the pregnancy, and should not be a cause for unnecessary anxiety.
2. Asma Khali &, Pranav Pandya; Screening for Down syndrome; The Journal of Obstetrics and Gynecology of India (2006)
3. Hsiao-Ching Yee et al.; Method for determining hCG levels in fluid samples; AmeriTek USA Inc; Google Patents
4. Low PAPP-A; Hampshire Hospitals (2016)
5. David S. Newberger; Down Syndrome: Prenatal Risk Assessment and Diagnosis; American Family Physician