Pregnancy and the Quad Marker Screen
The quad marker screen, similar to the triple marker screen, is a blood test that provides a woman and her health care provider with useful information about her pregnancy. The test predicts the likelihood of a certain problem occurring. It does not diagnose the problem. For example, cholesterol screening determines a person's risk for heart disease based on the amount of cholesterol in the blood, but it does not necessarily mean that the person has heart disease. The quad marker screen determines if a woman is at higher or lower risk of carrying a baby with a birth defect. This means that some women with healthy babies will have screening results indicating a possible problem (and will be offered appropriate follow-up testing), while some women whose babies have birth defects will go undetected.
Because of the uncertainties surrounding the test result, you can opt to not have it. Talk to your doctor about the pros and cons of taking this test before you make a final decision.
What Happens During the Quad Marker Screen?
During the quad marker screen, a sample of blood is taken from your vein. Substances in the blood sample are measured to screen for:
- Problems in the development of the fetus's brain and spinal cord, called open neural tube defects; the quad marker screen can predict approximately 75%-80% of open neural tube defects.
- Genetic disorders such as Down syndrome, a chromosomal abnormality; the quad marker screen can predict approximately 75% of Down syndrome cases in women under age 35 and over 80% of Down syndrome cases in women age 35 years and older.
When Should I Get a Quad Marker Screen?
Between 15 and 20 weeks of pregnancy, your health care provider may offer you a quad marker screen. The test can only be performed during the 15th and 20th week of pregnancy.
What Substances Are Measured During a Quad Marker Screen?
The blood sample is sent to a laboratory and tested for the presence of the following four substances, which are normally found in the baby's blood, brain, spinal fluid, and amniotic fluid:
- Alpha-fetoprotein (AFP): A protein produced by the baby's liver
- Unconjugated Estriol (UE): A protein produced in the placenta and in the baby's liver
- Human Chorionic Gonadotropin (hCG): A hormone produced by the placenta
- Inhibin-A: A hormone produced by the placenta
The expected amount of these substances normally found in the mother's bloodstream changes weekly during pregnancy, so it is important to tell your health care providers how far along you are in your pregnancy. High AFP levels may indicate that the baby has an open neural tube defect. High AFP levels may also indicate that the fetus is older than was thought or that the woman is expecting twins. Lower than normal AFP levels could indicate that a woman is at higher risk for having a baby with Down syndrome.
Levels of hCG and Inhibin-A are higher than normal when a woman has an increased risk of having a baby with Down syndrome. Lower than normal levels of estriol (a hormone) may also indicate that a woman is at high risk for having a baby with Down syndrome.