Alpha Fetoprotein

What is Alpha Fetoprotein?

Alpha Fetoprotein (AFP) is a protein produced by the liver, gastrointestinal tract and yolk sac of the developing fetus. The blood levels of Alpha Fetoprotein are high in the fetus, and steadily decline after birth to undetectable levels by 1 year.

What does the Alpha Fetoprotein Test indicate?

Alpha Fetoprotein is virtually undetectable in men and non-pregnant women. However, during pregnancy the protein crosses the placenta and is detectable in the mother’s blood. The maternal blood levels of Alpha Fetoprotein are used as indicators for developmental abnormalities such as Down’s Syndrome  and trisomy 18, or Open Neural Tube Defects such as Spina Bifida (holes along the spinal column) and anencephalogy (the absence of a large part of the brain and skull).

How is Alpha Fetoprotein Testing done?

Tests for Alpha Fetoprotein are done via maternal blood sampling and laboratory testing between 16 and 18 weeks. A high level of maternal Alpha Fetoprotein indicates that there is a potentially increased risk of open neural tube defects such as Spina Bifida. A low level of maternal Alpha Fetoprotein may indicate a potentially increased risk of a genetic abnormality such as Down’s Syndrome or Trisomy 18.

What do abnormal Alpha Fetoprotein results mean?

Most women who are at increased risk of having a baby with developmental or genetic defects will be offered the Alpha Fetoprotein test in addition to other protein makers of fetal development (See the Triple Screen and Quad Screen). The problem with the test for Alpha Fetoprotein is that it tends to have a high false positive rate. While this rate in and of itself is not a huge problem, the fact that many women go on to have unnecessary invasive tests such as amniocentesis or chorionic villus sampling is a cause for concern. These tests slightly increase a woman’s chance of miscarrying and if the tests aren’t necessary, mother and baby have been put at risk for nothing.  Often the real cause of an elevated AFP result may be incorrect age of the fetus, a multiple pregnancy or even maternal diabetes.

What should Mama do?

While most obstetricians have not completely abandoned the blood test for Alpha Fetoprotein, with newer more sensitive and specific prenatal screening tests available, obstetricians are opting to use other more sensitive and specific prenatal screening tests  to look for fetal abnormalities.  Ask your obstetrician, especially if you have abnormal blood levels of Alpha Fetoprotein, if another more sensitive and specific screening test can be done to screen for genetic and developmental abnormalities or to confirm your results.