Triple or Quad Screening for Birth Defects

Topic Overview

What is the triple or quad screening?

The triple screening measures the amounts of three substances in a pregnant woman's blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and estriol (uE3). When a test for the hormone inhibin A is added, it's called a quad screening. These tests are also called the maternal serum triple or quad test, the expanded AFP test, the AFP plus test, or the multiple marker screening test.

The amounts of these substances help your doctor find out the chance that your baby has certain birth defects, such as Down syndrome, spina bifida, or anencephaly. These tests 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.

The triple or quad screening is usually done at 15 to 20 weeks of pregnancy.

Each substance tested in a triple or quad screening gives you different information about possible problems. Together, these results give the best information. These screening tests look for the amount of:

• Alpha-fetoprotein (AFP) , which is made by the baby's liver.
• Human chorionic gonadotropin (hCG) , a hormone made by the placenta when a woman becomes pregnant.
• Estriol (uE3) , a form of estrogen that increases during pregnancy. It is produced in large amounts by the placenta.
• Hormone inhibin A , a protein produced by the baby and the placenta.

Your doctor will look at the levels of these substances-along with your age and other factors-to see if your baby has a higher-than-average chance of having a birth defect.

How is it done?

A simple blood test is all that's needed for these tests.

The health professional taking a sample of your blood will:

• Wrap an elastic band around your upper arm. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure on the site and then put on a bandage.

How accurate is it?

A screening test shows the chance that a baby has a certain birth defect. The accuracy of a screening test is based on how often the test correctly finds a birth defect.

• The triple and quad tests correctly find neural tube defects, such as spina bifida, in 80 out of 100 fetuses who have it and find anencephaly in about 90 out of 100 fetuses.^{footnote 1} The tests miss spina bifida in 20 out of 100 fetuses who have it and miss anencephaly in 10 out of 100 fetuses.
• The triple test correctly finds Down syndrome in 69 out of 100 fetuses who have it. It misses the condition in 31 out of 100 fetuses.^{footnote 2}
• The quad test correctly finds Down syndrome in 81 out of 100 fetuses who have it. It misses Down syndrome in 19 out of 100 fetuses.^{footnote 2}

With the triple or quad test, there is a chance of getting a false-positive test result. This means that the test could show a problem when the baby doesn't have the problem. A false positive may be more likely with the triple screening than the quad screening.

A false-positive result can cause stress and lead to unnecessary testing (such as an amniocentesis). Many women 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 he or she does have a birth defect. (This is a false-negative test result.)

Your doctor will use your age and your baby's age to interpret the test results. If your test results are abnormal, your doctor may use a fetal ultrasound to make sure of your baby's age.

What do the results mean?

A "positive" result means that there is a higher-than-average chance your baby has a birth defect. If the result is "negative," or normal, it means that your baby probably doesn't have a birth defect. But it doesn't guarantee that you will have a normal pregnancy or baby.

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.

What do you do with the results?

If you have a positive test result, your doctor may want you to have the diagnostic test amniocentesis to find out for sure if there is a problem. But it's your choice whether to have another test.

If you have a negative result, you may choose not to have another test.

Should you have the triple or quad screening?

Deciding whether to have a test for birth defects is a personal decision. And it can be a hard choice. You need to think about what the results of a test would mean to you and how they might affect your choices about your pregnancy.

If you choose to have a test, you may want to talk with a genetic counselor. The counselor can talk with you about the reasons to have or not have the test. He or she can also help you find other resources for support and decision-making.

For more help on deciding about having a triple or quad screening, see the topic:

• Pregnancy: Should I Have Screening Tests?