Quad Screening

What is Quad Screening?

Quad Screening is a prenatal test to determine the likelihood that a fetus (unborn baby) is affected with trisomy 21 (Down syndrome), trisomy 18, and certain types of birth defects (open neural tube defect or abdominal wall defects). Chromosome abnormalities (e.g. trisomy 21, trisomy 18) occur more frequently as a woman ages. If the test indicates an increased risk for one of these disorders, further testing with ultrasound and amniocentesis are available.

When and how is Quad Screening performed?

Quad Screening is performed between 15 to 20 weeks of pregnancy (counting from the first day of the last menstrual period). A blood sample is taken and four hormone and protein levels (alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), estriol, and inhibin) are measured. These levels are combined with the woman's age, gestational age and ethnicity to calculate the chance that the fetus has trisomy 21 or trisomy 18. The test also determines if the fetus is at increased risk for an open neural tube defect or an abdominal wall defect, or Smith-Lemli-Opitz syndrome (SLO), a rare genetic condition. Test results are available in approximately one week.

Does Quad Screening detect all chromosome abnormalities?

No. There are many different chromosome abnormalities; approximately half are trisomy 21 or trisomy 18. Quad screening identifies approximately 80% of fetuses with trisomy 21 and 67% of fetuses with trisomy 18. Diagnostic testing (CVS or amniocentesis) will identify 99% of all chromosome abnormalities. These procedures have a small risk of pregnancy loss.

What if my Quad Screening result is screen positive (abnormal)?

If the test result is positive, it does not mean that the fetus has a problem. It does mean, however, that the chance of the fetus having a chromosome abnormality, birth defect or SLO is increased and that further testing should be considered. Sometimes there are other explanations for why the test result is screen positive, such as the estimated gestational age is incorrect (either you are further along or not as far along as expected) or there are twins. Our genetic counselors are available to discuss your Quad Screening test results and options for further testing.

What if my Quad Screening result is screen negative (reassuring)?

If the result is negative, the chance the fetus has a chromosome abnormality or certain birth defect (open neural tube defect, abdominal wall defect) is low. A negative test result is reassuring but does not rule out all chromosome abnormalities, birth defects or genetic conditions.

If you are interested in Quad Screening, contact your healthcare provider to arrange this blood test.