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Alpha-Fetoprotein (AFP) Test

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What is an alpha-fetoprotein (AFP) test?

Alpha-fetoprotein (AFP) is a protein produced in the liver of a developing fetus. During a baby’s development, some AFP passes through the placenta and into the mother’s blood. An AFP test measures the level of AFP in pregnant women during the second trimester of pregnancy. Too much or too little AFP in a mother’s blood may be a sign of a birth defect or other condition. These include:

  • A neural tube defect, a serious condition that causes abnormal development of a developing baby’s brain and/or spine
  • Down syndrome, a genetic disorder that causes intellectual disabilities and developmental delays
  • Twins or multiple births, because more than one baby is producing AFP
  • Miscalculation of the due date, because AFP levels change during pregnancy

Other names: AFP Maternal; Maternal Serum AFP; msAFP screen

What is it used for?

An AFP blood test is used to check a developing fetus for risk of birth defects and genetic disorders, such as neural tube defects or Down syndrome.

Why do I need an AFP test?

The American Pregnancy Association says that all pregnant women should be offered an AFP test sometime between the 15th and 20th week of pregnancy. The test may be especially recommended if you:

  • Have a family history of birth defects
  • Are 35 years or older
  • Have diabetes

What happens during an AFP test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

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Will I need to do anything to prepare for the test?

You don’t need any special preparation for an AFP test.

Are there any risks to the test?

There is very little risk to you or your baby with an AFP blood test. You may have slight pain or bruise at the spot where the needle was put in, but most symptoms go away quickly. Another test called amniocentesis provides a more accurate diagnosis of Down syndrome and other birth defects, but the test has a small risk of causing a miscarriage.

What do the results mean?

If your results show higher than normal AFP levels, it may mean your baby has a neural tube defect such as spina bifida, a condition in which the bones of the spine don’t close around the spinal cord, or anencephaly, a condition in which the brain does not develop properly.

If your results show lower than normal AFP levels, it may mean your baby has a genetic disorder such as Down syndrome, a condition that causes intellectual and developmental problems.

If your AFP levels are not normal, it doesn’t necessarily mean there is a problem with your baby. It may mean you are having more than one baby or that your due date is wrong. You may also get a false-positive result. That means your results show a problem, but your baby is healthy. If your results show a higher or lower than normal level of AFP, you will likely get more tests to help make a diagnosis.

Is there anything else I need to know about an AFP test?

AFP tests are often part of a series of prenatal tests called multiple markers or triple screen tests. In addition to AFP, a triple screen test includes tests for hCG, a hormone produced by the placenta, and estriol, a form of estrogen made by the fetus. These tests can help diagnose Down syndrome and other genetic disorders.

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If you are at higher risk for having a baby with certain birth defects, your provider may also recommend a newer test called cell-free DNA (cfDNA).  This is a blood test that can be given as early as the 10th week of pregnancy. It can show if your baby has a higher chance of having Down syndrome or certain other genetic disorders.

References

  1. American Pregnancy Association [Internet]. Irving (TX): American Pregnancy Association; c2017. Maternal Serum Alpha-Fetoprotein Screening (MSAFP) [updated 2016 Sep 2; cited 2017 Jun 5]; [about 3 screens]. Available from: http://americanpregnancy.org/prenatal-testing/maternal-serum-alpha-fetoprotein-screening
  2. American Pregnancy Association [Internet]. Irving (TX): American Pregnancy Association; c2017. Triple Screen Test [updated 2016 Sep 2; cited 2017 Jun 5]; [about 3 screens]. Available from: http://americanpregnancy.org/prenatal-testing/triple-screen-test/
  3. Graves JC, Miller KE, Sellers AD. Maternal Serum Triple Analyte Screening in Pregnancy. Am Fam Physician [Internet]. 2002 Mar 1[cited 2017 Jun 5]; 65(5):915–921. Available from: https://www.aafp.org/afp/2002/0301/p915.html
  4. Johns Hopkins Medicine [Internet]. Johns Hopkins Medicine; Health Library: Common Tests During Pregnancy [cited 2017 Jun 5]; [about 3 screens]. Available from: http://www.hopkinsmedicine.org/healthlibrary/conditions/adult/pregnancy_and_childbirth/common_tests_during_pregnancy_85,p01241
  5. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2019. Maternal Serum Screening, Second Trimester; [updated 2019 May 6; cited 2019 Jun 4]; [about 2 screens]. Available from: https://labtestsonline.org/tests/maternal-serum-screening-second-trimester
  6. Lab Tests Online [Internet]. American Association for Clinical Chemistry; c2001–2017. Glossary: Spina Bifida [cited 2017 Jun 5]; [about 3 screens]. Available from: https://labtestsonline.org/glossary/spina-bifida
  7. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2017. Prenatal Diagnostic Testing [updated  2017 Jun; cited 2019 June 4]; [about 3 screens]. Available from: http://www.merckmanuals.com/home/women-s-health-issues/detection-of-genetic-disorders/prenatal-diagnostic-testing
  8. National Center for Advancing Translational Sciences/Genetic and Rare Diseases Information Center [Internet]. Gaithersburg (MD): U.S. Department of Health and Human Services; Neural Tube Defects [updated 2013 Nov 6; cited 2017 Jun 5]; [about 3 screens]. Available from: https://rarediseases.info.nih.gov/diseases/4016/neural-tube-defects
  9. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What Are the Risks of Blood Tests? [updated 2012 Jan 6; cited 2017 Jun 5]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests#Risk-Factors
  10. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What To Expect with Blood Tests [updated 2012 Jan 6; cited 2017 Jun 5]; [about 4 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2017. Health Encyclopedia: Alpha-fetoprotein(AFP) [cited 2017 Jun 5]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=90&contentid;=P02426
  12. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2017. Health Encyclopedia: Alpha-fetoprotein(Blood) [cited 2017 Jun 5]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid;=alpha_fetoprotein_maternal_blood
  13. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2017. Health Information: Alpha-Fetoprotein (AFP) in Blood [updated 2016 Jun 30; cited 2017 Jun 5]; [about 5 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/alpha-fetoprotein-afp-in-blood/hw1663.html
  14. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2017. Health Information: Triple or Quad Screening for Birth Defects [updated 2016 Jun 30; cited 2017 Jun 5]; [about 5 screens]. Available from: https://www.uwhealth.org/health/topic/special/maternal-serum-triple-or-quadruple-screening-test/ta7038.html#ta7038-sec
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