Quad Marker Screen Test (cont.)

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How accurate is the test?

The test is a screening test only, and is not 100% accurate. It can predict about 75% to 80% of open neural tube defects, problems with the development of the baby's brain and spinal cord. It predicts about 80% of fetuses with Down syndrome in women over age 35 and about 75%  in younger women. The fact that it is not 100% accurate means that not all women who have a positive high risk result on the quad screen will have a fetus with a birth defect, and the test may also be normal even in the presence of birth defects.

For example, about 50 women out of every 1,000 will have a result on the quad screen that indicates an increased risk of a birth defect, but only one to two of those women will actually have a baby with an open neural tube defect. About 40 women out of 1,000 will have a result indicating an increased risk of Down syndrome, but only one to two of these women will have a baby with Down syndrome.

Who should receive the test?

The test should be offered to all pregnant women who desire to have the test. It is done between the 15th and 20th week of gestation, most commonly between the 16th and 18th weeks. Because of some of the uncertainty surrounding the test, not all women choose to have the test. Most doctors particularly recommend the test for women older than 35 years of age, women with type 1 diabetes, and in women that have a family history of birth defects.

What does an abnormal result mean?

As with any screening test, an abnormal result does not mean that the fetus definitely has a birth defect or genetic condition. It only means that the blood levels of these four substances suggest that a woman's risk is increased of having a baby with certain conditions. Women who have a result suggesting increased risk are typically offered further testing. This can include repeating the quad screen and/or having a high definition ultrasound examination to look for signs of birth defects or abnormalities in the developing baby. If this testing is abnormal, the mother may be offered the choice to undergo amniocentesis. Amniocentesis involves withdrawing a sample of amniotic fluid for genetic and chromosome testing, and it can definitively establish the diagnosis of genetic and chromosomal problems in most fetuses. Amniocentesis carries a small risk of miscarriage (less than 1% of fetuses tested).

REFERENCE: American Pregnancy Association. Quad screen.


Medically Reviewed by a Doctor on 8/14/2013

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