Quadruple Marker Test

 The Quad Screen Test: What You Need to Know

The quad what? 

The quad screen — also called the maternal serum screen — is a prenatal screening test that analyzes four substances in your blood. (Thank Latin for that — quad means four.) It’s usually carried out between your 15th and 22nd week of pregnancy.

The quad screen can tell you if your baby has an increased chance of:

· Down syndrome

· trisomy 18 (Edwards Syndrome)

· neural tube defects

· abdominal wall defects

It does so in part by measuring these four substances:

· alpha-fetoprotein (AFP), a protein produced by your baby’s liver

· human chorionic gonadotropin (hCG), a hormone produced by your placenta

· Estriol (uE3): a hormone made by your placenta and the baby’s liver. Estriol is the highest amount of circulating hormone in a woman’s blood while she’s pregnant. Low levels of this hormone are associated with increased risk for Down syndrome and trisomy 18.

· inhibin A, a third hormone produced by your placenta. Doctors don’t know exactly the role this protein plays in pregnancy. But they do know that it increases the reliability of the sequential screening test. High levels are associated with Down syndrome while low levels are associated with trisomy 18.

Yup, pregnancy is a heavy hormone-production 9 months. Now you can stop wondering why you’ve been feeling so tired!

Should you get the quad screen test? 

This is an optional test, which means you don’t have to do it. But many doctors recommend it for all pregnant women. Here’s what might make you opt in:

· You’re 35 or older. Since the test is noninvasive, if you’re worried about your baby’s health only because of your age, this test is a good option.

· Your family has a history of developmental irregularities at birth (e.g., spina bifida, cleft palate).

· You’ve already had a child with developmental irregularities at birth.

· You have type 1 diabetes.

Keep in mind that the quad screen doesn’t just look at the results of your blood test. It adds in different factors — such as your age, ethnicity, and weight — and then estimates the chances that your baby may have an abnormality.

The screen doesn’t tell you that there’s definitely a problem; if abnormal, it tells you that you should have further testing.

How the results are determined 

By now, you’ve realized that each week of pregnancy is different than the week before. (The 10 jars of pickles you asked for last week are now probably being used as door stoppers.) That means that the levels of AFP, hCG, estriol, and inhibin A in your blood are also changing week by week.

That’s why it’s important to make sure you’ve told your OB how far along you are in your pregnancy. By using an automated analyzer and a software package, doctors can screen your blood and calculate the chances of serious disorders.

What the results mean

Want to take a deep breath before we look at what the results could mean? You’re right, thinking about these conditions can be downright scary. However, even if your quad screen is positive (meaning that there are higher chances that your baby could have one of these conditions), it doesn’t necessarily mean that your baby will be affected. It just means that the chances are higher.

If you’re thinking, “Huh?” here’s an example: About 4 percent of quad screens will return positive for an increased risk of Down syndrome, but only about 1 to 2 percent of those babies will have Down syndrome. Breathe out now.

Let’s skirt round the exact numbers and get to the nitty gritty according to the Cleveland Clinic:

· Higher than normal AFP levels could mean that your baby has an open neural tube defect such as spina bifida or anencephaly. On the other hand, they could also mean that he’s older than you thought or that — guess what — you’re expecting twins.

· Lower than normal AFP, hCG, and inhibin A levels could mean that you have higher chances of having a baby with Down syndrome or trisomy 18.

· Lower than normal levels of estriol may also mean that you have higher chances of having a baby with Down syndrome or trisomy 18.

More on the conditions

· Down syndrome is a genetic condition that comes from extra genetic material (the 21st chromosome). Approximately 1 in 700 babies is born with Down syndrome.

· Trisomy 18 is a genetic condition that comes from extra chromosome number 18. Most trisomy 18 pregnancies result in miscarriages or stillbirth; babies who are born, live for only a few years. About 1 in 5,000 babies is born with this condition.

· Neural tube defects include conditions like spina bifida or anencephaly. Spina bifida is when the brain, spinal cord, or the spinal cord’s protective covering doesn’t develop properly. Anencephaly means that the baby’s brain doesn’t form completely. Neural tube defects occur in 1 or 2 out of every 1,000 births.

How accurate is the quad screen test? 

· The test can detect approximately 75 percent of Down syndrome cases in women under age 35 and 85 to 90 percent of Down syndrome cases in women age 35 years and older. Remember, though, that most people who are told they have an increased risk of having a Down syndrome baby don’t end up having a baby with Down syndrome.

· It can also detect approximately 75 percent of open neural tube defects.

· If the quad screen test is negative, there’s still a possibility that your baby could be born with one of these conditions.

Further testing after a positive quad screen test

What happens if you have a positive quad screen test? First, remember that many women who show positive test results go on to have babies that are just fine.

The next step is a consultation with a genetic counselor, and together you’ll decide whether further testing is right for you. Sometimes this means another quad screen test and a high definition (targeted) ultrasound. And then, if the results are still positive, you may want to do the following tests:

· Prenatal cell-free DNA screening. This blood test examines cell-free DNA coming from your placenta and your baby and found in your bloodstream.

· Chorionic villus sampling (CVS). A sample of tissue from the placenta is removed for testing.

· Amniocentesis. A sample of amniotic fluid is drawn for testing.

The downside here is that both CVS and amniocentesis pose a slight threat for miscarriage.