What is the quad marker screening test?
The quad marker screening test (quad screen) is a blood test administered in pregnancy, typically between the 15th and 20th weeks of gestation. Similar to the triple screen, the quad marker screen provides information about whether there is an increased risk for certain birth defects in the baby. The test is simple and involves taking a blood sample as for any other routine blood test. The quad marker test is a screening test, meaning that it gives information about risk, but it does not allow the definitive diagnosis of any conditions. It can only signal that further testing should be done to confirm a diagnosis. There is no risk to the baby from the test.
What substances are measured in the test?
The quad screen looks at the three substances also measured in the triple screen (alpha-fetoprotein, human chorionic gonadotropin, and estriol) test plus one additional substance, inhibin A.
- Alpha-fetoprotein (AFP) is produced by the liver of the fetus
- Human chorionic gonadotropin (hCG) is a hormone made by the placenta
- Estriol is an estrogen made both by the placenta and the liver of the fetus
- Inhibin-A is another hormone made by the placenta
Looking at levels of these four substances in the mother's bloodstream allows an estimation of risk for neural tube defects and certain chromosomal abnormalities, like Down syndrome.