Pregnancy and the Quad Marker Screen

The quad marker screen, similar to the triple marker screen, is a blood test that provides a woman and her health care provider with useful information about her pregnancy. The test predicts the likelihood of a certain problem occurring. It does not diagnose the problem. For example, cholesterol screening determines a person's risk for heart disease based on the amount of cholesterol in the blood, but it does not necessarily mean that the person has heart disease. The quad marker screen determines if a woman is at higher or lower risk of carrying a baby with a birth defect. This means that some women with healthy babies will have screening results indicating a possible problem (and will be offered appropriate follow-up testing), while some women whose babies have birth defects will go undetected.

Because of the uncertainties surrounding the test result, you can opt to not have it. Talk to your doctor about the pros and cons of taking this test before you make a final decision.

What Happens During the Quad Marker Screen?

During the quad marker screen, a sample of blood is taken from your vein. Substances in the blood sample are measured to screen for:

  • Problems in the development of the fetus's brain and spinal cord, called open neural tube defects; the quad marker screen can predict approximately 75%-80% of open neural tube defects.
  • Genetic disorders such as Down syndrome, a chromosomal abnormality; the quad marker screen can predict approximately 75% of Down syndrome cases in women under age 35 and over 80% of Down syndrome cases in women age 35 years and older.

When Should I Get a Quad Marker Screen?

Between 15 and 20 weeks of pregnancy, your health care provider may offer you a quad marker screen. The test can only be performed during the 15th and 20th week of pregnancy.

What Substances Are Measured During a Quad Marker Screen?

The blood sample is sent to a laboratory and tested for the presence of the following four substances, which are normally found in the baby's blood, brain, spinal fluid, and amniotic fluid:

  • Alpha-fetoprotein (AFP): A protein produced by the baby's liver
  • Unconjugated Estriol (UE): A protein produced in the placenta and in the baby's liver
  • Human Chorionic Gonadotropin (hCG): A hormone produced by the placenta
  • Inhibin-A: A hormone produced by the placenta

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The expected amount of these substances normally found in the mother's bloodstream changes weekly during pregnancy, so it is important to tell your health care providers how far along you are in your pregnancy. High AFP levels may indicate that the baby has an open neural tube defect. High AFP levels may also indicate that the fetus is older than was thought or that the woman is expecting twins. Lower than normal AFP levels could indicate that a woman is at higher risk for having a baby with Down syndrome.

Levels of hCG and Inhibin-A are higher than normal when a woman has an increased risk of having a baby with Down syndrome. Lower than normal levels of estriol (a hormone) may also indicate that a woman is at high risk for having a baby with Down syndrome.

Is the Quad Marker Screen Safe?

Yes. The quad marker screen is a safe and useful screening test for families concerned about birth defects or genetic diseases. It is a test that carries no risk to the baby, since a blood sample is taken only from the mother.

What Does It Mean if the Quad Marker Screen Results Are Normal?

Normal levels of AFP, estriol, hCG, and Inhibin-A strongly indicate that you have a healthy pregnancy and a healthy baby. In over 98% of pregnancies, normal quad marker screen results predict healthy babies and births without major complications. However, there are no prenatal tests that can guarantee your baby and pregnancy will be completely healthy or without complications.

What Does It Mean if the Quad Marker Screen Results Are Abnormal?

Quad marker screen results that are not in the normal range do not necessarily mean there is a problem in your pregnancy.

The quad marker screen is used as a screening tool only, which means it can only assess your risk of having a baby with a certain birth defects (it is not used to diagnose the particular problem that may be present). If the quad marker screen results are not in the normal range, further tests such as an ultrasound or amniocentesis may be necessary.

Out of 1,000 pregnant women, approximately 50 will have quad marker screen results that indicate an increased risk for having a baby with a birth defect. Of those 50 women, only one or two will actually have a baby with an open neural tube defect. About 40 women will have quad marker screen results that show an increased risk for having a baby with Down syndrome and one or two will actually have a baby with Down syndrome.

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Should I Have the Quad Marker Screen?

It is recommended that all pregnant women have a quad marker screen, but it is your decision whether or not to have the test. However, if you have any of the following risk factors, you may strongly want to consider having the test:

  • You are age 35 or older when the baby is due
  • Your family has a history of birth defects
  • You've had a child with a previous birth defect
  • You were diagnosed with type 1 diabetes prior to your pregnancy

If you have any concerns about the test, talk to your doctor or health care provider.

WebMD Medical Reference Reviewed by Trina Pagano, MD on September 17, 2014

Sources

SOURCES: 

The March of Dimes. 

Deborah A. Driscoll, MD, "Second trimester maternal serum screening for fetal open neural tube defects

and aneuploidy." American College of Medical Genetics, 2004.

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