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Triple Screen or Quad Screen

Also known as: Triple test; AFP Maternal; msAFP; Quad Screen; 4-marker screen
Formal name: Triple Screen [with AFP (alpha-fetoprotein), hCG (human chorionic gonadotropin) and uE3 (unconjugated estriol)]; Quadruple Screen [with the addition of inhibin A]
Related tests: hCG; Estrogen; First Trimester Down Syndrome Screen

The Test Sample

What is being tested?

The triple screen is a group of three tests that are used to screen pregnant women in the second trimester of pregnancy. The quad screen adds a fourth test to the group. Each test that is performed measures a different substance found in the blood: AFP, hCG, unconjugated estriol, and with the quad – inhibin A. The newest marker, inhibin A, increases both the sensitivity and specificity of the screen.

  • Alpha-fetoprotein (AFP) is a protein produced by fetal tissue. During development, AFP levels in fetal blood and amniotic fluid rise until about 12 weeks, and then levels gradually fall until birth. Some AFP crosses the placenta and appears in the maternal blood.
  • Human chorionic gonadotropin (hCG) is a hormone produced by the placenta. Levels in maternal blood rise for the first trimester of pregnancy and then fall to less than 10% by the end of pregnancy.
  • Unconjugated estriol (uE3) is a form of estrogen that is produced by the fetus through metabolism. This process involves the liver, adrenals, and the placenta. Some of the unconjugated estriol crosses the placenta and can be measured in the mother’s blood. Levels rise around the 8th week and continue to increase until shortly before delivery.
  • Inhibin A is a hormone produced by the placenta.  Inhibin is a dimer (has 2 parts) and is sometimes referred to as DIA or dimeric inhibin A. Levels in maternal blood decrease slightly from 14 to 17 weeks gestation and then rise again.

In pregnancies where the fetus is carrying the chromosomal defect that results in Down syndrome (trisomy 21), the levels of AFP and unconjugated estriol tend to be low and hCG and inhibin A levels high.

In pregnancies where the fetus has trisomy 18, unconjugated estriol and hCG levels are low and AFP levels can be variable.

A baby with an open neural tube defect has an opening in its spine, head, or abdominal wall that allows higher-than-usual amounts of AFP to pass into the mother’s blood. The other markers are not used in the evaluation of risk for carrying a fetus with a neural tube defect.

How is the sample collected for testing?

Blood is drawn from a vein in your arm. All four tests (AFP, hCG, unconjugated estriol, and inhibin A) can be done on the same tube of blood.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.