Alpha-Fetoprotein (AFP) Test - Triple Marker Test

Test Name

Alpha-Fetoprotein (AFP) Test - Triple Marker Test (Biochemical Screening).

Procedure Timing

The Alpha-Fetoprotein (AFP) Test, also known as the Triple Marker Test, is typically performed between weeks 16-20 of pregnancy, with the optimal time being between weeks 16-18. The precise timing will be determined by the attending physician.

Purpose of the Test

Fetal proteins are produced in the fetal liver and pass in minimal quantities into the amniotic fluid and then through the placental barrier into the maternal circulation. This test assesses the risk of the fetus suffering from conditions such as Down syndrome (trisomy 21, which causes characteristic physical features and intellectual disabilities), or defects in the central nervous system (such as anencephaly - absence of brain tissue, or spina bifida - severe spinal cord malformation).

What is Tested

The blood sample is tested for the following markers:

• Alpha-fetoprotein (AFP)
• Human chorionic gonadotropin (hCG)
• Estriol (E3)

Interpreting the Test Results

The risk of Down syndrome is calculated based on maternal age and the levels of the three markers in the blood. A high level of maternal serum alpha-fetoprotein raises suspicion of a defect in the fetal central nervous system.
If the calculated risk is higher than 1:380 or if the levels of maternal serum alpha-fetoprotein are significantly elevated, further targeted evaluations of the nervous system and amniotic fluid analysis for chromosomal abnormalities are recommended. This test can detect approximately 60% of fetuses with Down syndrome.

Additional Tests

In recent years, additional tests have been introduced to improve the accuracy of prenatal screening and reduce the rate of false-positive results:

• Quadruple marker screening, which includes the Triple Marker Test plus the hormone Inhibin, increases accuracy to approximately 70%.
• Combined screening, which includes the nuchal translucency measurement and assesses the hormones PAPP-A and hCG.
• Integrated screening, which combines various screenings and includes nuchal translucency, E3, hCG, PAPP-A, and Inhibin. This test achieves an accuracy level of 80-90% or higher.