What is alpha-fetoprotein test?

An alpha-fetoprotein (AFP) test is a blood test that measures the amount of AFP present in blood. It’s usually part of what’s called a triple screen or quad screen in the second trimester of pregnancy. However, it can also be useful for adults who aren’t pregnant.The yolk sac, GI tract, and liver of an unborn baby produce AFP. It then circulates through the fetal and maternal blood.

Why do I need an alpha-fetoprotein test?

An AFP test is a routine screening test that’s given to expectant mothers between the 14th and 22nd weeks of their pregnancy. It is most accurate between the 16th and 18th weeks, so it’s important to know exactly when you became pregnant.

AFP testing is usually part of triple marker. This screening exam also tests your levels of:

  • human chorionic gonadotropin (HCG)
  • estriol, which is a hormone produced by your placenta and your baby’s liver
  • inhibin A, which is a hormone produced by your placenta

The AFP test is especially important for women who are at high risk of having children with birth defects, including women:

  • who are 35 or older
  • with a family history of birth defects
  • who used harmful medications or drugs during their pregnancies
  • who have diabetes

Too much or too little AFP in a mother's blood may be 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 due date, because AFP levels change during pregnancy
What do the test 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.

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