What is a Double Marker Test?
A Double Marker Test is a prenatal screening test performed during pregnancy to assess the risk of chromosomal abnormalities such as Down syndrome and trisomy 18. The test involves measuring the levels of two markers in the mother’s blood, one of which is a hormone produced by the placenta (Human Chorionic Gonadotropin or hCG) and the other is a protein (pregnancy-associated plasma protein-A or PAPP-A). The results of the test, combined with other factors such as the mother’s age and the ultrasound findings, are used to calculate the risk of chromosomal abnormalities in the fetus.
Why Double Marker Test?
Double Marker Test is performed during pregnancy to assess the risk of chromosomal abnormalities in a developing fetus. The test measures the levels of two pregnancy-associated biomarkers in the mother’s blood: alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG). Abnormal levels of these markers can indicate an increased risk for conditions such as Down syndrome, neural tube defects, and other chromosomal abnormalities. The test is usually performed between the 15th and 20th weeks of pregnancy, and it is typically combined with ultrasound to provide a more comprehensive assessment of the fetus’s health.
Down’s Syndrome:
Down syndrome (also known as Down’s syndrome) is a genetic disorder caused by the presence of an extra copy of chromosome 21. It affects physical and intellectual development, causing characteristic physical features and intellectual disabilities. People with Down syndrome often have intellectual disabilities with an IQ in the mild to moderate range, although this can vary widely. Some common physical features include a flat facial profile, small head, short neck, and upward slanting eyes. Despite these challenges, people with Down syndrome can lead happy and fulfilling lives with the support of their families and communities.
Trisomy 18:
Trisomy 18, also known as Edwards syndrome, is a genetic disorder caused by the presence of an extra chromosome 18 in a baby’s cells. This results in intellectual disability, physical abnormalities, and a high rate of infant mortality. Many babies with Trisomy 18 die before birth or within their first few months of life, and those who survive often have serious health problems that require ongoing medical care. There is no cure for Trisomy 18, but treatments can help manage symptoms and improve quality of life.
The test is often most recommended for women who:
The test is often most recommended for women who are considered to be at higher risk for chromosomal abnormalities, such as those who:
- Are 35 years or older
- Have a family history of genetic disorders
- Have had previous pregnancies with chromosomal abnormalities
- Have had a previous pregnancy with a neural tube defect
- Have had an abnormal result from a previous screening test such as an ultrasound or a serum screening test.
It is important to note that this test is optional, and the decision to have it should be made after discussing the potential benefits and limitations with a healthcare provider.
The science behind the double marker test
The science behind the double marker test involves measuring the levels of two specific biomarkers in the mother’s blood during pregnancy: alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG).
AFP is a protein produced by the fetus and is normally present in the mother’s blood in small amounts. An abnormal increase in AFP levels can indicate the presence of chromosomal abnormalities or neural tube defects.
hCG is a hormone produced by the placenta and is present in the mother’s blood during pregnancy. Abnormal levels of hCG can indicate an increased risk for chromosomal abnormalities.
By measuring the levels of both AFP and hCG, the double marker test can provide a preliminary assessment of the risk of chromosomal abnormalities in the developing fetus. However, it is important to note that the test results are not diagnostic and are typically combined with other tests, such as ultrasound, to provide a more comprehensive assessment of the fetus’s health.
The procedure of double marker test
The procedure for the double marker test involves taking a blood sample from the mother and measuring the levels of alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG) in her blood.
The procedure typically takes the following steps:
- The mother will have a blood sample taken from a vein in her arm.
- The blood sample will be sent to a laboratory for analysis.
- The laboratory will measure the levels of AFP and hCG in the blood sample and calculate the risk of chromosomal abnormalities in the developing fetus.
- The results of the test will be reported to the healthcare provider, who will interpret the results and discuss them with the mother.
It is important to note that the procedure is non-invasive and poses no risk to the mother or the fetus. The results of the test are typically available within a few days to a week.
Risks associated with the double marker test
The double marker test is a relatively safe and non-invasive test, and there are generally few risks associated with the procedure. However, some potential risks to consider include:
False positive results: In some cases, the test may indicate an increased risk of chromosomal abnormalities when none actually exist. This can lead to unnecessary anxiety for the mother and can also result in additional tests and procedures being performed.
False negative results: In some cases, the test may indicate a low risk of chromosomal abnormalities when in fact the fetus has a chromosomal abnormality. This can result in a false sense of security for the mother.
Pain or discomfort during blood collection: Some women may experience discomfort or pain when having blood drawn from a vein in their arm.
Emotional distress: The results of the test and the possibility of a chromosomal abnormality can cause emotional distress for the mother.
It is important to discuss the potential benefits and limitations of the double marker test with a healthcare provider, and to weigh the potential risks against the potential benefits before making a decision about having the test.
Result of double marker test
The results of the double marker test can provide information about the risk of chromosomal abnormalities in a developing fetus. The results are typically reported as a multiple of the median (MoM) value, which compares the level of the markers in the mother’s blood to the average level in a reference population of women with normal pregnancies.
A MoM value greater than 2.0 or less than 0.5 can indicate an increased risk of chromosomal abnormalities, although this does not confirm the presence of a chromosomal abnormality. An abnormal result from the double marker test should be followed up with additional tests, such as chorionic villus sampling (CVS) or amniocentesis, to confirm the presence of a chromosomal abnormality.
A normal result from the double marker test does not guarantee that the fetus is free of chromosomal abnormalities, as the test has a limited ability to detect all chromosomal abnormalities. Therefore, it is important to discuss the results of the test with a healthcare provider, who can interpret the results and provide additional information and recommendations based on the individual case.