Quad screen in pregnancy: Importance and accuracy

The quad screen test is done during the second trimester of pregnancy or between weeks 15 and 18. This procedure is also called the quadruple marker test.

The quad screen measures levels of alpha-fetoprotein (AFP), a protein produced by the liver of the developing baby. Aside from that, it also measures levels of human chorionic gonadotropin (HCG) and Inhibin A.

These are hormones made by the placenta. In addition, this procedure also measures estriol, a hormone produced by the placenta and the baby’s liver. These proteins and hormones are four important substances found in pregnant women’s blood. 

Why is a quad screen test essential in pregnancy?

According to Mayo Clinic, a quad screen test is done during the second trimester of pregnancy to help detect if your baby has a risk of birth disorders like down syndrome and trisomy 18.

Another thing, this can help identify if the baby has a risk of birth defects such as spina bifida and abdominal wall defects. 

Down syndrome, also called trisomy 21 is a chromosomal disorder. This may cause your baby lifelong intellectual difficulty and developmental delays. In some cases, babies with down syndrome also experience other health problems. 

Your doctor might consider combining the results of your first-trimester screening with your quad screen test. To be more accurate in the detection of your baby’s risk of down syndrome.

On the other hand, an abdominal wall defect occurs when your baby’s intestines or other abdominal organs stick through the belly button.

Moreover, spina bifida is a birth defect in the spinal cord and the spine. It happens when the portion of the neural tube fails to develop and close correctly. 

An article written by Web MD clarified that this procedure does not directly diagnose the problem but rather the likelihood of it. That means a positive result from a quad screen test does not necessarily mean that your baby has a disorder or birth defects. Your doctor may recommend an appropriate follow-up test if the result is positive.

Likewise, a negative quad screen test result doesn’t guarantee that your baby is completely safe from having chromosomal disorders or birth defects. 

What to expect during a quad screen test?

Here are the things you should expect if you are in the second trimester of your pregnancy and are preparing to take a quad screen test:

• Your doctor might provide or ask you to have genetic counseling before the quad test.
• Before the quad test, you can eat and drink normally.
• During a quad test, a sample of your blood is taken from the vein in your arm using a needle.
• The blood sample is sent to be analyzed in a lab
• You may go back to your usual activities immediately while waiting for the result to come out.

Remember, a positive result from the quad screen test only means that levels of some or all the four substances in the blood sample were outside the normal range.

You may undergo an additional test to form a more accurate diagnosis. Keep in mind that other factors can affect the levels of those substances.

Your weight, race, and a miscalculation of how long you have been pregnant can affect the result of your quad test. Aside from that, the result can be affected too if you are pregnant with more than one baby or have been pregnant through in vitro fertilization.

Additionally, having diabetes and smoking during pregnancy are also factors that can affect the quad screen result.

This prenatal screening test is guaranteed safe. It will not cause miscarriage or any pregnancy complications. However, the possible result may cause anxiety for the expectant mom. It is important to ask your doctor to help you understand the result of your tests.

Who should take the quad screen test?

You may opt to undergo the quadruple marker test if you want to be screened for any risk of having a baby with neural tube defects and chromosomal disorder during pregnancy.

It depends on your preference whether you want to do a quad screen test or not. But it is recommended for all pregnant women. However, you are more at risk of having a baby with a chromosomal disorder or birth defects if you are any of the following:

1. Diagnosed with type 1 diabetes even before pregnancy.
2. Have any family member that has a congenital disability.
3. Have had an older child who has a birth defect.
4. Age 35 years old or older.
5. Had a viral infection during pregnancy.
6. Have been exposed to high levels of radiation.
7. Used harmful drugs while pregnant.

It is highly suggested to take the quadruple marker screening if you have a high risk of having a baby with congenital disorder.

Understanding the result

The baby has a high risk of having a neural tube defect if the levels of alpha-fetoprotein are higher than expected. It may mean that your baby has spina bifida or anencephaly.

However, factors such as inaccurate calculation of how long you have been pregnant may raise the level of AFP. Carrying a twin can affect the result too.

On the other hand, AFP levels that are lower than the normal range could mean that you have a higher risk of having a baby with down syndrome.

In addition, low levels of estriol could also indicate a high risk of having a baby with down syndrome. You have a high risk of having a baby with down syndrome too when the levels of hCG and Inhibin-A in your sample blood are higher than expected.

It is essential to consult your doctor to further explain the result of your quad screen test. They might recommend follow-up testing to have a more accurate diagnosis.

Another test that you may consider

• Your doctor may recommend a targeted ultrasound if your quad screen result is positive in having a high risk of neural tube defects in your baby. However, this procedure is not effective in detecting down syndrome during pregnancy.
• Prenatal cell-free DNA screening determines if your baby is at risk of down syndrome. This procedure examines cell-free DNA from the placenta and the fetus.
• Your doctor may recommend a procedure called Amniocentesis to diagnose both congenital neural tube defects and chromosomal disorders. In this process, a sample of amniotic fluid is taken from the uterus for testing. However, this procedure is a little dangerous because it poses a risk of miscarriage.
• Chorionic villus sampling can help diagnose down syndrome and other chromosomal conditions. But cannot be used to detect neural tube defects. And it also poses a slight risk of miscarriage like amniocentesis. It is because this procedure is done by getting a sample of tissue from the placenta.

Reasons for further testing

Undergoing further testing helps you confirm the first diagnosis from the result of the quad screen test. Validating the diagnosis can help you decide what to do next.

If both quad screen and other test results are positive, you can pursue interventions such as fetal surgery for a neural tube defect. You can also start to plan for your child’s special needs and address expected lifestyle changes.

A confirmed diagnosis can help you make decisions about carrying your baby to term. You can also identify support groups and resources that may help you throughout pregnancy.

However, some parents do not allow any testing that poses any risk of miscarriage or harming the baby such as chorionic villus sampling and amniocentesis. It is essential to discuss with your doctor the risks and benefits of any tests before agreeing to perform further testing.

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