Double Marker Pregnancy Test: Everything You Need To Know
Pregnancy is a miraculous time for every woman. To ensure the maternal and fetal well being it is vital to consult with a gynaecologist throughout your pregnancy. There are several tests used to check nutrient levels, the progress of your baby’s growth and also screen for possible genetic conditions.
(Just to be sure if you are pregnant, Here are 10 Methods for Pregnancy Test At Home (With Toothpaste, Salt, Sugar etc))
These tests vary from country to country depending on the conditions that are prevalent in each place. Today we will discuss the importance of the double marker screening test.
What is a dual marker screening test?
A double marker screening test is one that is conducted in the first trimester, primarily, between the 10th to 13th week of pregnancy. A blood sample is taken to measure the levels of β hCG (human chorionic gonadotropin hormone) and the PAPP - A (pregnancy-associated plasma protein). This test is used to detect the likelihood of having a child with Down syndrome. It is commonly done in women over the age of 35, as there is an increased chance of having a child with Down syndrome as the maternal age increases.
What is Down syndrome?
In the medical world, Down syndrome is known as trisomy genetic disorder. Each cell is made up of 46 chromosomes, that is 23 pairs of chromosomes. To make a fetus two cells with 23 chromosomes each have to unite (the sperm and the egg) to make a whole 46 pair zygote, which later becomes the fetus. In some cases, during cell division, an extra pair of chromosome gets transferred among one of the chromosome pairs. So instead of two, there are three chromosomes. In Down syndrome, the 21st pair has three chromosomes instead of two. This anomaly manifests as the common physical and cognitive features observed with Down syndrome.
The dual marker screening test helps to determine this condition by checking for markers that are altered if a fetus with this extra chromosome is present. These markers can also be used to detect other trisomies, namely, Edward syndrome (trisomy of chromosome 18) and Patau syndrome (trisomy of chromosome 13). Since these are quite rare when compared to Down syndrome, they are not commonly discussed.
(Also read about this woman’s story - Down's Syndrome Never Stopped Me From Exploring Life)
What are the indications for such a screening test?
Most pregnant women in their first trimester have to undergo the dual marker screening test. There are a few risk factors that increase a woman’s chance of having a child with Down or other genetic conditions. These include:
- Age over 35 years
- History of insulin-dependent diabetes
- Previous child born with Down’s syndrome (or similar genetic conditions)
- Family history of birth defects.
- IVF pregnancy
- Current weight during pregnancy
What does a normal test result look like?
The first thing to remember is that this is a screening test. This means that even if a positive result is shown it doesn’t mean that your child has Down syndrome. The whole purpose of doing a screening test is to figure out whether further more expensive tests are required or not.
A β hCG value falling in the range of 25700 - 288000 mIU/ ml is considered normal.
A normal PAPP - A result in the first trimester is usually a value that is greater than 0.5 MoM.
What if my test results are not within the normal ranges?
During the first trimester, β hCG levels rise exponentially. It is after the first trimester that the levels begin to fall. Until then it is not unusual to find your hCG levels in the thousands. A substantial increase outside the normal range has been linked as a marker for possible genetic conditions such as Down syndrome. High levels of β hCG are also observed in twin pregnancies, molar pregnancies and in women who are on fertility medications.
Coupled with a high β hCG value, having a low PAPP - A value is usually considered as a positive double marker screening test. When a physician receives this result, they conduct further tests to confirm a diagnosis of a genetic condition.
Some of the more diagnostic and confirmatory tests include amniocentesis and chorionic villus sampling. These are invasive and are used to test the cells of the baby in the amniotic sac.
Are there any other tests that are done during this time?
While taking the double marker test most doctors also screen ultrasonographically for an increased risk of Down syndrome. This is usually known as NT test (or a nuchal translucency test). This is an ultrasonographic marker that is used in combination with β hCG and PAPP A.
Nuchal translucency basically measures the amount of fluid present in your baby’s neck. On its own this test doesn’t produce any significant results, however, the accuracy of diagnosing Down syndrome increases to about 75 - 80% when combined with a dual marker screening test.
A NT value lower than 3.5 mm is considered normal.
What are some of the advantages and disadvantages of this procedure?
Since this test is conducted in the first trimester, it is an early screening test that helps to assess genetic conditions. This gives you ample time to decide on further tests and further screening tests that can be done as the pregnancy progresses. It is fairly accurate in diagnosing Down syndrome and similar genetic conditions.
While it is accurate, triple and quadruple screening test provides more accuracy as they analyze more markers within the blood. The accuracy increases up to 88 - 90% with a quadruple screening test. Tests conducted later in pregnancy always give a much better picture of any fetal abnormalities. The main disadvantage, however, would be the cost of the procedure. It can be expensive for some considering physician fees, hospital bills, prenatal supplements and other tests required during the course of pregnancy.
So what is the cost to have a dual marker screen done?
It highly depends on where you get the test done. Some smaller labs can charge as low as INR 1300, but more sophisticated labs can charge as much as INR 5000.
Every test has its own importance and significance during pregnancy. It is always best to discuss the pros and cons of each test with your gynaecologist before going for it. When you do receive the results talk to your doctor about any doubts that you have. If the test is positive, wait for confirmation from your doctor before panicking. Positive results on screening tests rarely turn out to have positive results in confirmatory tests.
Always have a support system. When getting these tests done, take your partner or a member of your family along with you. Any result, positive or negative can be daunting. So it is always great to have someone to help you through the process, even if it is just to calm your nerves. Whatever the results, discuss future plans for your pregnancy with your primary caregiver.
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