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:

  • neural tube defect is a serious condition that causes abnormal development of a developing baby’s brain and/or spine

  • Down syndrome, is 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.

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 you 35 years or older

  • Have diabetes


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.


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. 


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.