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Alpha fetoprotein AFP LabTest

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Alpha-fetoprotein (AFP) LabTest

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 sign of a birth defect or other condition. These include:

  • 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 due date, because AFP levels change during pregnancy

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

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

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
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.

There is very little risk to you or your baby with an AFP blood test. You may have slight pain or bruising 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.

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.

  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: http://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]. American Association for Clinical Chemistry; c2001–2017. Second Trimester Maternal Serum Screening: Common Questions [updated 2017 Feb 3; cited 2017 Jun 5]; [about 5 screens]. Available from: https://labtestsonline.org/understanding/analytes/second-trimester-screening/tab/faq
  6. Lab Tests Online [Internet]. American Association for Clinical Chemistry; c2001–2017. Second Trimester Maternal Serum Screening: The Test [updated 2017 Feb 3; cited 2017 Jun 5]; [about 4 screens]. Available from: https://labtestsonline.org/understanding/analytes/second-trimester-screening/tab/test
  7. Lab Tests Online [Internet]. American Association for Clinical Chemistry; c2001–2017. Second Trimester Maternal Serum Screening: The Test Sample [updated 2017 Feb 3; cited 2017 Jun 5]; [about 3 screens]. Available from: https://labtestsonline.org/understanding/analytes/second-trimester-screening/tab/sample
  8. 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
  9. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2017. Prenatal Diagnostic Testing [cited 2017 June 5]; [about 3 screens]. Available from: http://www.merckmanuals.com/home/women-s-health-issues/detection-of-genetic-disorders/prenatal-diagnostic-testing
  10. 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
Alpha-fetoprotein (AFP) LabTest

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