Quad Marker For Genetic Defects And Trisomy 18

December 29, 2022 by No Comments

The quad marker test is another name for the Quadruple test. The quad marker screen is a blood test that can help you figure out whether you’re pregnant. It can help you figure out how likely your kid is to have Down syndrome, Edward’s syndrome (trisomy 18), or neural tube abnormalities.

What is a Quad Marker /Quadruple Test?

A blood test called a Quad Screen or Quadruple Marker is performed during the second trimester (15-20 weeks) of pregnancy to detect chromosomal abnormalities and birth problems in the unborn baby.

  • AFP (alpha-fetoprotein):  A protein produced by the developing infant.
  • HCG (human chorionic gonadotropin):  A  hormone produced by the placenta.
  • Estriol: is a hormone produced by the placenta and the liver of the infant.
  • Inhibin A: Another hormone produced by the placenta.

During your second trimester, you may have a quad screen, also known as a quad marker screen. The term “quad” refers to the fact that your blood is tested for four different parameters. The quad test is used to determine the likelihood of bearing a baby with Edwards syndrome (trisomy 18), Down syndrome (trisomy 21), Spina bifida, or Anencephaly.

A routine prenatal screening test is the quadruple marker screening test. There’s no chance of miscarriage or other pregnancy issues with this test. It is optional to take the quadruple marker screening test. The findings of the tests only indicate if you are at a higher chance of having a kid with Down syndrome, not whether your baby has the disorder. If the risk level is moderate or high, you can choose to combine the quad test with a more decisive test.

Must read: NIPT Test and its 7 Important advantages

Why quad screen test is important?

During the second trimester, your healthcare professional will ask if you want a quad marker screen. The screening will take place between the 15th and 20th weeks of your pregnancy, counting from the beginning day of your last menstrual period. Between the 16th and 18th weeks, you’ll get the most accurate results.

If you are 35 years old or older, your healthcare practitioner may recommend a quad screen.

  • During pregnancy, you had a viral infection.
  • Have a history of hereditary problems in your family (birth defects).
  • Have been exposed to excessive radiation levels.
  • Diabetic and insulin administration
  • Use of harmful medications or drugs in pregnancy

Is the quad marker screen safe, and how does it work?

A small amount of blood is drawn during the quad screen. A lab technician takes a small amount of blood from one of your veins to do the test. It is completely safe for your child and just necessitates a single needle poke for the mother.

What is the purpose of the quad screen?

A quad screen examines your blood for four things:

  1. AFP (alpha-fetoprotein): AFP is produced by your baby’s liver. If the levels are higher than predicted, the infant may have a neural tube defect such as spina bifida or anencephaly. However, you may be further along in your pregnancy than you imagined. It’s also possible that you’re expecting twins. Low AFP levels may indicate an increased risk of giving birth to a baby with Downs syndrome.

2. Unconjugated estriol (UE): A hormone produced by your baby and the placenta (the organ that feeds your child). Low levels suggest a greater chance of having a Down syndrome child.

3. Human chorionic gonadotropin (hCG): A hormone produced by the placenta and detected by the screening. Higher-than-expected levels could indicate a higher chance of having a baby with Down syndrome.

4. Inhibin-A: This is a protein produced by your placenta and ovaries. With higher-than-expected amounts of this protein, the probability of conceiving a baby with Down syndrome rises.

The levels of these compounds alter as your pregnancy progresses. These alterations alert the doctor to the possibility of a hereditary disease. It’s crucial to note that a positive quad marker test does not necessarily imply that the baby has a genetic disease but it only indicates that the risk is higher.

Why is it done?

The quad screen assesses your chances of having a child with one or more of the following conditions:

  • Down’s Syndrome

Down syndrome is a condition in which a person (trisomy 21). Down syndrome is a genetic condition that causes intellectual disabilities, developmental delays, and health difficulties in certain people throughout their lives.

downs syndrome
Fig 1: Downs syndrome
  • Trisomy 18

This is a chromosomal abnormality that results in significant developmental delays and body structural abnormalities. By the age of one, trisomy 18 is usually fatal.

  • Spina Bifida

Spina bifida is a kind of birth abnormality in which a section of the neural tube does not grow or seal properly, resulting in abnormalities in the spinal cord and spine bones.

  • Defects in the abdominal wall

The baby’s intestines or other abdominal organs stick through the birth canal in these birth abnormalities.

What does “normal quad screen” imply?

A normal quad marker test result indicates that you are not at increased risk of having a child with birth problems. Additional genetic tests are unlikely to be recommended by your doctor. No tests can guarantee a healthy baby or an easy pregnancy.

What does it signify when a test result is abnormal?

The quad screen is solely used to assess your risk. It does not reveal whether or not your child will be born with a genetic condition. As a result, an abnormal result may indicate that additional testing is required. It could also imply that your baby is older than you and your doctor expected.

If your quad screen reveals an increased risk, your doctor will recommend more tests. These tests can help you figure out if your child has a genetic condition. An ultrasound or amniocentesis may be recommended by your doctor.

amniocentesis process
Fig2: Amniocentesis process

In the case of a positive result, are there any other causes for the high levels of the four chemicals hCG, AFP, Inhibin A, and UE in the blood?

High levels of AFP in the blood can be caused by a variety of factors. The following are some causes.
·       The unborn child dies within the mother’s womb.
·       If any portion of the skull or brain is missing,   (Anencephaly)
·       The intestines or any of the surrounding organs are damaged (Duodenal atresia)
·       Tetralogy of Fallot or a cardiac defect.
·       Spina Bifida – kind of spinal deformity.
·       Turner’s syndrome 
·       A lady who is expecting more than one child.
·       High levels of inhibin A and hCG and low levels of estriol and AFP might be attributable to the following factors:
2. Edwards syndrome  (trisomy 18)
3. Down’s syndrome  (trisomy 21)

Is the Quad test for Down syndrome reliable?

The quad screen successfully identifies approximately 80% of mothers who are carrying a Down syndrome baby. A false-positive result occurs in about 5% of women, meaning the test result is positive but the baby does not have Down syndrome.

Is it necessary to fast for the quadruple test?

A quad screen test is a common prenatal screening test that takes a blood sample from the mother to examine the baby’s health and well-being. This test necessitates a simple blood test. There are no special measures to follow because it is a basic blood test. The woman can eat and drink as she normally would.

How can you lower your chances of having Down syndrome?

There is no way to avoid Down syndrome. You should visit a genetic counselor before becoming pregnant if you are at high risk of having a kid with Down syndrome or if you already have one child with Down syndrome. A genetic counselor can assist you in determining your odds of having a Down syndrome child.

What factors contribute to the development of Down syndrome?

The mother’s age is one factor that raises the chances of having a kid with Down syndrome. Women who become pregnant at the age of 35 or later are more likely to have a Down syndrome-affected pregnancy than women who fall pregnant at a younger age.