The quad screen test is a maternal blood screening test that looks for four specific substances: AFP, hCG, Estriol, and Inhibin-A.
AFP: alpha-fetoprotein is a protein that is produced by the fetus
hCG: human chorionic gonadotropin is a hormone produced within the placenta
Estriol is an estrogen produced by both the fetus and the placenta
Inhibin-A-is a protein produced by the placenta and ovaries
The quad screen is a maternal blood screening test which is similar to the Triple Screen Test.
The quad screen looks for not only the three specific substances evaluated in those tests (AFP, hCG, and Estriol) but also a fourth substance known as Inhibin-A.
The likelihood of identifying pregnancies at risk for Down Syndrome is higher through the evaluation of Inhibin-A levels, and false positive rate of the test is also lower.
The quad screen test involves drawing blood from the mother.
The quad screen test is performed between the 16th and 18th week of pregnancy.
All pregnant women should be offered the quad screen, but it is recommended for women who:
Have a family history of birth defects
Are 35 years or older
Used possible harmful medications or drugs during pregnancy
Have diabetes and use insulin
Had a viral infection during pregnancy
Have been exposed to high levels of radiation
The results are combined with the mother’s age and ethnicity in order to assess probabilities of potential genetic disorders.
High levels of AFP may suggest that the developing baby has a neural tube defect such as spina bifida or anencephaly.
The most common reason for elevated AFP levels is inaccurate dating of the pregnancy.
Low levels of AFP and abnormal levels of hCG and estriol may indicate that the developing baby has Trisomy 21(Down syndrome), Trisomy 18 (Edwards Syndrome) or another type of chromosome abnormality.
A screening test and not a diagnostic test in that it only notes that a mother is at risk of carrying a baby with a genetic disorder.
Many women who experience an abnormal test result go on to deliver healthy babies, and an abnormal test results warrant additional testing to make a diagnosis.