The quad screen — also known as the quadruple marker test or simply the quad test — is a prenatal test that measures levels of four substances in a pregnant woman's blood:
- Alpha-fetoprotein (AFP), a protein made by the developing baby
- Human chorionic gonadotropin (HCG), a hormone made by the placenta
- Estriol, a hormone made by the placenta and the baby's liver
- Inhibin A, another hormone made by the placenta
Typically, the quad screen is done between weeks 15 and 20 of pregnancy — the second trimester.
Results of the quad screen indicate your risk of carrying a baby who has certain chromosomal conditions, such as Down syndrome. The alpha-fetoprotein part of the test can help detect neural tube defects, such as spina bifida.
If your risk level is low, the quad screen can offer reassurance of a healthy pregnancy.
If your risk level is moderate or high, you might choose to follow the quad screen with another test that's more definitive.