During pregnancy, a developing fetus can have chromosomal abnormalities that may lead to various complications. Chromosomal abnormalities occur due to an incorrect number of chromosomes, the wrong amount of genetic information within a chromosome, or structural flaws in the chromosomes. These abnormalities can result in congenital anomalies, chromosomal disorders, or miscarriages. The double marker test helps to detect such chromosomal malformations in the fetus, which may result in developmental deformities in the child post-birth.
What is a Double Marker Test /Dual Marker Test in Pregnancy?
The double marker test or dual marker blood test, also known as maternal serum screening, is a predictive test that detects chromosomal abnormalities in the fetus of a pregnant woman. The test involves measuring the quantity of two markers, beta-human chorionic gonadotropin (ꞵ-hCG, a pregnancy-related hormone), and pregnancy-associated plasma protein A (PAPP-A) in the blood erythrocytes. Altered levels of these markers are often associated with a higher risk of chromosomal disorders. Doctors usually advise patients to undergo this test in the first trimester to detect any abnormalities early on, thus preventing several health problems in the child after birth.
What is the Need for a Double Marker Test During Pregnancy?
The double marker test helps in the early detection of chromosomal abnormalities present in the growing fetus. In a typical pregnancy, a female fetus has 22 pairs of XX chromosomes, while a male fetus has 22 pairs of XY chromosomes. However, in some rare cases, there may be an extra chromosome in some or all of the body cells, leading to a genetic condition called trisomy. Such fetuses have three copies of that chromosome instead of two, which may cause developmental and intellectual delays. The abnormalities arising due to trisomy are Down syndrome, Edwards's syndrome, and Patau’s syndrome. Hence, detecting chromosomal abnormalities through the double marker test can help safeguard the mother and her unborn baby.
Overall, the double marker test is a crucial tool for the early detection of chromosomal abnormalities in pregnancy, which helps prevent several health problems in the child after birth.
When Should a Double Marker Test be Performed in Pregnancy?
The double marker test is usually performed between the 8th and 14th weeks of pregnancy as part of a full-fledged screening panel. The blood sample for this test is collected between the 11th and 13th week, which is the ideal time for combined risk assessment. Doctors recommend this test for women above 35 years of age or those with birth defects in their family history as they are more likely to develop chromosomal abnormalities, which may lead to chromosomal malformations in the fetus.
Dual Marker Blood Test Normal Range and Cost:
The normal range of Beta hCG is 25,700-288,000 mIU/ml for all age groups, and the normal range of PAPP-A is 1 MoM for all age groups. The cost of a double marker test may vary among different cities and is usually between 2500 and 3500 INR.
Double Marker Test Procedure:
The double marker test is a prenatal screening test that involves a blood test and an ultrasound examination known as nuchal translucency (NT) scan. During the NT scan, clear tissue at the back of the baby's neck is examined to detect two markers, Beta hCG and PAPP-A, which are pregnancy-related hormones found in the mother's blood.
Beta hCG is a glycoprotein secreted by the placenta in a pregnant woman, and a higher value of this hormone is often associated with an increased risk of chromosomal disorders such as trisomy 18 or Down syndrome. In contrast, lower levels of PAPP-A, an important plasma protein, are linked to a higher risk of Down syndrome.
The double marker test helps detect three primary conditions that arise due to the addition of chromosomes in one or more cells. Down syndrome, also known as trisomy 21, is the most common trisomy, causing mental and physical challenges for the newborn. Trisomy 18 (Edward's syndrome) and Trisomy 13 (Patau's syndrome) also cause severe intellectual disability and physical defects in the baby.
Uses of Double Marker Test:
The double marker test helps determine whether the unborn baby has any risk of developing neurological abnormalities or mental disorders. It detects Down syndrome or Trisomy 21, Trisomy 18, and Trisomy 13, which cause mental and physical challenges in the baby.
Dual Marker Blood Test Results:
The test results can indicate whether there is a low, moderate, or high risk of abnormality. A low-risk or screen-negative result is normal and indicates that the baby has a low risk of having a chromosomal abnormality. However, a low-risk result does not ensure that the baby has absolutely no abnormality. If the results are moderate or high risk, further testing such as NIPT may be recommended to confirm the condition.
Dual Marker Blood Test Benefits:
The double marker test helps detect and prevent Down syndrome in newborns, as well as other deformities in the heart, lungs, stomach, intestines, and other organs. By detecting chromosomal abnormalities early on, parents can prepare themselves and their families for the challenges of raising a child with special needs.
In conclusion, the double marker test is an essential prenatal screening test that can detect chromosomal abnormalities in the unborn baby, allowing parents to make informed decisions about their pregnancy and plan for the future.
Interpretation of Double Marker Test Results
The double marker test results are typically presented in the form of ratios, which can indicate whether a pregnant woman is at low, moderate, or high risk of chromosomal abnormalities.
- Screen negative: If the ratio is 1:1000 or higher, the expectant mother is in a low-risk category, and the baby has a lower likelihood of having chromosomal malformations.
- Screen positive: If the ratio is between 1:10 and 1:250, the mother is in a high-risk category, and the baby has a higher chance of developing chromosomal abnormalities. Continuing with the pregnancy with test-positive results can increase the risk of fetal death during delivery.
Double Marker Test vs. NT Scan
When performed together in the first trimester, the double marker test and NT scan can provide the most accurate results. The NT scan creates real-time images of the baby, allowing for precise measurements of the neck and nasal bone to identify abnormalities, which, when combined with blood results and age-related risk, can assess the baby's potential risk of Down syndrome, trisomy 13, or trisomy 18.
Dual Marker Blood Test - FAQs
Q1. Do I need to do anything if the double marker test is positive?
Ans. If the test results are positive, doctors may recommend additional diagnostic tests like amniocentesis or chorionic villus sampling to detect the exact problem.
Q2. What is the normal range for a double marker test in pregnancy?
Ans. The normal range for ꞵ-hCG is between 25,700 and 2,88,000 mlU/ml on a double marker test.
Q3. How accurate is the double marker test?
Ans. This test is frequently recommended as it is a fairly accurate way of detecting chromosomal malformations, with a sensitivity of around 70%.
Q4. What are the risks associated with the double marker test?
Ans. The double marker test is a non-invasive routine blood test with no associated risks.
Q5. Should a double marker test be done on an empty stomach?
Ans. This test is a non-fasting blood test. One can eat or drink normally before the test unless instructed by a healthcare professional.
Q6. What are chromosomal abnormalities in pregnancy?
Ans. A chromosomal abnormality happens when there is an incorrect amount or number of DNA within a chromosome or a structurally faulty chromosome in the fetus.
Q7. Is the double marker test mandatory?
Ans. The test is not mandatory. However, it is recommended by doctors to do the test if the expecting mother is above 35 years of age or has an elevated risk of chromosomal issues.
Q8. When is the double marker test recommended?
Ans. The ideal time for the test is the first trimester of the gestation period.
Q9. What is the difference between the double marker and triple marker test?
Ans. There is no difference between the double-marker and triple-marker tests. The double marker test is performed within the first 13 weeks of pregnancy, while the triple marker test is conducted after 13 weeks.