The double marker test, also known as the dual marker test or dual screening test, is a prenatal screening test performed during pregnancy to assess the risk of certain chromosomal abnormalities, especially Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18). It combines two blood tests: the measurement of certain hormones and proteins in the mother’s blood.
Here’s how the double marker test generally works:
- Time: The test is usually done between 10 and 14 weeks of pregnancy, but it can also be done up to 20 weeks.
- Blood samples: The mother’s blood is sampled to measure two specific substances: pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG).
- Analysis: PAPP-A and hCG levels are measured, and the results are compared to established reference ranges. Deviations from these categories may indicate an increased risk of chromosomal abnormalities.
- Risk calculation: Test results are used along with the mother’s age, gestational age and other factors to calculate the risk of Down syndrome and Edwards syndrome in the fetus.
It is important to note that the double marker test is a screening test, not a diagnostic test. It provides an estimate of risk, but it cannot confirm the presence or absence of a chromosomal abnormality with certainty. If the test indicates a high risk, further diagnostic tests, such as amniocentesis or chorionic villus sampling (CVS), may be recommended to obtain a definitive diagnosis.
When Is the Double Marker Test in Pregnancy Required?
A double marker test is not required in pregnancy, but it is an alternative screening test offered to assess the risk of certain chromosomal abnormalities.
- Maternal Age: Advanced maternal age is associated with a higher risk of chromosomal abnormalities. This test may be recommended more often for women who are 35 years of age or older at the time of delivery.
- Family history: If there is a family history of genetic disorders or chromosomal abnormalities, healthcare providers may suggest considering a double marker test as part of the prenatal screening process.
- Previous screening results: If previous screening tests, such as ultrasound or biochemical markers, have shown high risk or raised concerns, a double marker test may be recommended to provide additional information.
- Personal choice: Ultimately, the decision to undergo a double marker test is personal. Some women may choose to get tested for peace of mind or to be prepared for a possible outcome.
Why is a Double Marker Test in Pregnancy Conducted?
Double marker tests in pregnancy are conducted to assess the risk of chromosomal abnormalities, especially Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18).
How Is a Double Marker Test in Pregnancy Conducted?
The double marker test in pregnancy is conducted by taking a blood sample from a pregnant woman to measure pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG) levels. The results are then analyzed along with other factors to calculate the risk of chromosomal abnormalities in the fetus.
Double marker test cost
The cost of a double marker test can vary depending on factors such as the reputation of the institution, the accuracy of the test, the sensitivity of the equipment used, and the specific requirements of the testing machines. On an average, a double marker test costs around Rs 2,500 to Rs 4,000. However, it is important to note that these figures are approximate and may vary in different locations.
What is Considered a Normal Range for a Double Marker Test in Pregnancy?
The normal range of double marker tests may vary depending on factors such as the laboratory and the testing method used. Generally, for pregnant women, the normal range of hCG (human chorionic gonadotropin) in all age groups is usually reported to be between 25,700 and 288,000 mIU/mL. As far as PAPP-A (pregnancy-associated plasma protein-A) is concerned, the normal value for women of all age groups is often defined as 1 MoM (multiple of the median).
Difference between double marker and triple marker test
Both double marker test and triple marker test are prenatal screening tests that are used to assess the risk of certain chromosomal abnormalities in the developing fetus. However, they differ in terms of the number of markers they evaluate and the specific conditions for which they are screened. Here are the details of the differences:
Double Marker Test:
- Markers: The double marker test evaluates two markers in the mother’s blood: pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG).
- Conditions examined: The double marker test primarily assesses the risk of two chromosomal abnormalities: Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18).
Triple Marker Test:
- Markers: The triple marker test evaluates three markers in the mother’s blood: alpha-fetoprotein (AFP), estriol, and hCG.
- Conditions examined: The triple marker test assesses the risk of chromosomal abnormalities similar to the double marker test (Down syndrome and Edwards syndrome). Additionally, it also checks for neural tube defects such as spina bifida.
Aspect | Double Marker Test | Triple Marker Test |
Number of Markers | 2 (PAPP-A and hCG) | 3 (AFP, estriol, and hCG) |
Chromosomal Abnormalities screen | Down syndrome (Trisomy 21) and Edwards syndrome (Trisomy 18) | Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and neural tube defects (e.g., spina bifida) |
Coverage | Evaluates two specific markers | Evaluates three specific markers |
Neural Tube Defects | Does not screen for neural tube defects | Screens for neural tube defects (e.g., spina bifida) |
Relevance | Older test, replaced by newer and more comprehensive tests like the quadruple marker test and the NIPT. | Older test, replaced by newer and more comprehensive tests like the quadruple marker test and the NIPT. |
FAQs
If the double marker test is positive, indicating an increased risk for chromosomal abnormalities, further diagnostic tests such as amniocentesis or chorionic villus sampling (CVS) may be recommended to confirm the presence of the abnormality. These diagnostic tests can provide a definitive diagnosis and more accurate information about the condition of the fetus.
No, a positive result of a double marker test does not guarantee that your child has a chromosomal abnormality. The double marker test is a screening test that assesses the risk of certain chromosomal abnormalities such as Down syndrome and Edwards syndrome.