The quad screen — also known as the quadruple marker test, the second trimester screen 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

Ideally, the quad screen is done between weeks 15 and 18 of pregnancy — the second trimester. However, the procedure can be done up to week 20.

The quad screen is used to evaluate whether your pregnancy has an increased chance of being affected with certain chromosomal conditions, such as Down syndrome. The alpha-fetoprotein part of the test can help evaluate the chance for neural tube defects, such as spina bifida, and abdominal wall defects, such as omphalocele.

If your risk level is low, the quad screen can offer reassurance that there is a decreased chance for Down syndrome, trisomy 18, neural tube defects and abdominal wall defects. If the quad screen indicates an increased chance of one of these conditions, you might consider additional screening or testing.

Oct. 21, 2015