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.

Oct. 13, 2012