The quad screen is a blood test that measures four substances produced by the fetus and the placenta that pass into a mother's bloodstream:[1]
- Alpha-fetoprotein (AFP), a protein made by the baby
- Human chorionic gonadotropin (hCG), a hormone created by the placenta
- Estriol, a form of estrogen produced by the placenta and baby
- Inhibin A, a hormone made by the placenta
Entering the results from a quad screen into a formula can help predict the likelihood of a chromosomal abnormality — specifically:
- Neural tube defects: High levels of AFP may suggest the possibility (but by no means the probability) that a baby is at higher risk of neural tube defects, including spina bifida.
- Chromosomal abnormalities: Low levels of AFP and abnormal levels of the other markers may indicate that the developing baby may be at higher risk for Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18).
Like other prenatal screenings, the quad screen does not provide a conclusive answer to whether or not a child has a genetic abnormality; it can only tell you whether the likelihood is more or less than the typical risk at your age.
When is the quad screen test done?
Because the quad screen is less accurate than the nuchal translucency (NT) screening combined with first trimester blood work, it's typically only recommended for women who are already in their second trimester, between week 15 and week 22 of pregnancy.[2] It's usually done in conjunction with the NT.
Who should have the quad screen?
Your doctor may recommend a quad screen instead of noninvasive prenatal testing (NIPT), a more accurate form of prenatal testing, because NIPT may not be available in your area or your insurance may not cover it.
More About Prenatal Testing
If you do have NIPT, you should still get a quad screen as well because the quad provides information about open neural tube defects.
How is the quad screen done?
A simple blood test is performed. Generally, one needle stick will yield all the blood needed for testing.
How accurate is the quad screen?
When an abnormality exists, the quad screen can detect an increased risk for approximately 85 percent of neural tube defect cases, about 80 percent of Down syndrome cases and 80 percent of trisomy 18 cases. It is important to keep in mind that this screen is not very accurate for testing other chromosomal abnormalities.
The false-positive rate for the independent quad screen is also very high: Only 1 or 2 out of 50 women with abnormally high AFP readings eventually prove to have an affected fetus. In the other 48 or 49, further testing reveals that there actually is no abnormality after all.
Hormone levels may be abnormal because there's more than one fetus, the fetus is either a few weeks older or younger than originally thought, or the results of the test were inaccurate or misinterpreted. An abnormal quad screen does not mean that your baby has a chromosomal abnormality; it means that the risks are increased and that you will need extra testing.
Keep in mind that if NIPT is available to you, it also only involves a blood draw, and the results are more accurate.
Are there any risks associated with the quad screen test?
No. Because the quad screen requires only a blood sample, it's completely safe. The only possible risk is that you may get a false-positive or a false-negative result.
What happens if you get an abnormal quad screen result?
Before you consider taking any action on the basis of prenatal screening, ensure an experienced physician or genetic counselor has evaluated the results. If you're carrying only one fetus and the ultrasound shows the estimated due date is correct, your doctor may offer amniocentesis as a follow-up.
Studies indicate that women who receive abnormal results on their quad screen but receive normal results on follow-up testing such as amniocentesis may still be at very slightly increased risk of certain pregnancy complications, such as small-for-gestational-age fetus, preterm delivery or preeclampsia. If you receive results like this, ask your practitioner about whether this might apply to you.
Yes 
No 
Trending On What to Expect
