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Quad Screening for Birth Defects

Test Overview

The quad screening is a blood test that may be done at 15 to 20 weeks 6 days of pregnancy. It's used to look for possible problems with your baby. The quad screening measures the amounts of four things in your blood. They are:

  • Alpha-fetoprotein (AFP). AFP is made in the liver of an unborn baby (fetus).
  • Human chorionic gonadotropin (hCG). This hormone is made by the placenta when you become pregnant.
  • Estriol (uE3). This is a form of estrogen that increases during pregnancy. It's made in large amounts by the placenta.
  • Hormone inhibin A. This hormone is produced by the baby and the placenta.

This test can't show for sure that your baby has a birth defect. You would need a diagnostic test called amniocentesis to find out for sure if there is a problem.

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Why It Is Done

The quad screening is done to find out the chance that your baby has Down syndrome, Trisomy 18, or a neural tube defect, such as spina bifida, or anencephaly.

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How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

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Results

A "positive" result for a problem means that there is a higher-than-average chance your baby has that problem. If the result is "negative," or normal, it means that your baby is less likely to have the problems that are screened for in the quad screening test. But it doesn't guarantee that you will have a normal pregnancy or baby.

The accuracy of a quad screening test is based on how often the test correctly finds a birth defect.

  • It correctly finds neural tube defects, such as spina bifida, in up to 80 out of 100 fetuses who have it. It finds anencephaly in about 95 out of 100 fetuses. The test misses spina bifida in at least 20 out of 100 fetuses who have it. And the test misses anencephaly in about 5 out of 100 fetuses who have it.footnote 1
  • It correctly finds Down syndrome in 81 out of 100 fetuses who have it. It misses Down syndrome in 19 out of 100 fetuses who have it.footnote 2

Your doctor may tell you the result of your test as a set of numbers. Doctors often use a certain number as a cutoff for a positive result. For example, your doctor may say the cutoff is 1 out of 200. This means that if your result is 1 out of 200 or 1 out of a number less than 200 (such as 1 out of 100), you have a positive result and your baby has a higher chance of a birth defect. If your result is 1 out of 300, this means that you have a negative result and your baby has a lower chance of a birth defect.

With the quad test, there is a chance of getting a false-positive test result. This means that the test could be positive when the baby doesn't have the problem.

A false-positive result can cause stress and lead to tests you don't need (such as an amniocentesis). Many people who have a positive screening test result are actually carrying a healthy baby.

Sometimes negative test results can be wrong too. They may show that the baby is fine when they do have a problem. (This is a false-negative test result.)

References

Citations

  1. American College of Obstetricians and Gynecologists (2017). Neural tube defects. Practice bulletin No. 187. Obstetics and Gynecology, 130(6): e279–e290. DOI: 10.1097/AOG.0000000000002412. Accessed December 13, 2019.
  2. American College of Obstetricians and Gynecologists (2016). Screening for fetal aneuploidy. ACOG Practice Bulletin No. 163. Obstetrics and Gynecology, 127(5): e123–e137. DOI: 10.1097/AOG.0000000000001406. Accessed April 6, 2017.

Credits

Adaptation Date: 2/24/2022

Adapted By: Alberta Health Services

Adaptation Reviewed By: Alberta Health Services

Adapted with permission from copyrighted materials from Healthwise, Incorporated (Healthwise). This information does not replace the advice of a doctor. Healthwise disclaims any warranty and is not responsible or liable for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.