How Does Immunity Change During Pregnancy?
March 10, 2026
- All it takes is just a drop of saliva
1. What is the quad screen?
A quad screen is a blood test which indicates your pregnancy has the possibility of a baby who might have a birth defect.
2. What does the quad screen test for?
The quad screen tests for four substances in a pregnant woman’s blood which are related to birth defects:
a. Alpha-fetoprotein (AFP) a protein produced by the fetus
b. Human chorionic gonadotropin, (hCG) a hormone produced by the placenta.
c. Estriol (uE3) is a form of estrogen produced by the fetus and the placenta. It is an estrogen found only during pregnancy.
d. Inhibin A, a hormone produced in the corpus luteum of the ovary. It suppresses follicle stimulating hormone (FSH).
3. When during pregnancy is the quad screening test done?
Usually, the quad screen is performed between 15 and 22 weeks of pregnancy. The most accurate results are produced between 16 and 18 weeks.
4. What does the quad screen show?
The quad screen can indicate the possibility of Down’s syndrome, (trisomy 21), Edwards syndrome (trisomy 18), and neural tube defects (NTDs)
5. What’s the difference between a diagnostic test and a screening test?
A screening test will tell you whether or not you have a chance (or sensitivity) of having a certain condition. A diagnostic test will tell you whether or not you actually have the condition (specificity).
6. What do the screening test results mean?
The quad screen results will be positive or negative for the risk of your baby having one of these four birth defects. These screening results don’t tell you that your baby actually has these conditions, but rather measures the risk (sensitivity) that your baby will have the condition. A diagnostic test, indicates whether or not you actually have a specific condition. A positive quad screen test result simply indicates a more than the average risk of one of these possible birth defects. A negative result indicates a lower than average risk for those birth defects.
Sensitivity refers to the ability to detect conditions. Specificity refers to the ability to detect a particular disease and rule out other possible diseases.
7. What happens if I have a positive quad screen?
With positive quad screen results, you have two choices. You can be concerned for the rest of your pregnancy whether your baby might have one of the birth defects screened for, or you can have have an actual diagnostic test for the birth defects. The diagnostic test for these four birth defects is an amniocentesis. Amniocentesis can be done as early as 12 to 13 weeks, but because it is invasive, it is considered riskier than the NIPT. However, these alternative tests for possible abnormalities are relatively new and can be extremely expensive. The three most common alternative tests include:
What is the non-invasive prenatal test (NIPT)?
Usually done at about 10 weeks, The NIPT test is a maternal blood test which analyzes the mother’s blood for fetal DNA. This is a screening test and can give results which could indicate trisomy 13 (Turner syndrome), trisomy 18 (Edwards syndrome), and trisomy 21 (Downs syndrome), XO (Turner syndrome), and a number of other possible problems such as congenital heart defects and structural malformations. Although 98 percent accurate, this is a screening test, not a diagnostic test, and many babies which screen positive with NIPT will be normal at birth.
What is the chorionic villus sampling (CVS) test?
Usually performed from 10 to 13 weeks, the CVS test is a diagnostic test and takes samples of tissue from the placenta. Since procuring tissue from the placenta is invasive, there is some risk for miscarriage as there is with amniocentesis.
What is the nuchal translucency plus blood work test?
Usually performed around 10 to 13 weeks, this test is a combination of an ultrasound measurement of the back of the neck of the baby plus tests of the mother’s blood. The ultrasound of the baby will show any fluid-filled spaces at the back of the baby’s neck. Between the ultrasound and the test of the mother’s blood, this screen shows the risk for chromosomal abnormalities.
What is the danger of a false negative test result?
As with any test, there is the possibility of a false negative result, that is, of the test failing to report a condition which is actually present. There is a one percent chance of a false negative from a quad screen, which means the screen could miss the presence of the risk for conditions such as trisomy 21, trisomy 18 or neural tube defects.
8. Is it important for know the difference between a screening test and a diagnostic test?
It is extremely important that you know the limits of whatever screen or test you are undergoing. Explaining this difference to you should be a part of your first prenatal visit. It is the obligation of your doctor to explain to you the difference between a screening test and a diagnostic test in a way you can understand.
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