What is an alpha-fetoprotein (AFP) test?

An AFP test is a blood test that measures the level of alpha-fetoprotein (AFP) in your blood when you are pregnant. The test checks your baby's risk of having certain birth defects and genetic problems, but it does not diagnose any health conditions. The test is usually done between 15 and 20 weeks of pregnancy.

AFP is a protein mostly made in your developing baby's liver. Usually, some AFP passes from the baby into your blood. But certain medical conditions can make the baby's body release more or less AFP than usual. When this happens, your AFP blood levels will be higher or lower than normal. Abnormal AFP levels may be a sign that your baby has an increased risk of a health problem, such as:

• A neural tube defect, a serious condition that happens when a baby's brain, spine and/or spinal cord do not form properly.
• Down syndrome, a genetic disorder that changes the way a baby's body and brain develop. It can cause both mental and physical health challenges. These problems may range from mild to severe.
• Edwards syndrome (trisomy 18), an uncommon genetic condition that causes an abnormal head shape and many organ defects. Most babies with this condition die in the first year of life.

For people who aren't pregnant, an AFP blood test may be used to help diagnose certain cancers, especially liver cancer. When the test is used this way, it's called an AFP tumor marker test.

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

What is it used for?

An AFP blood test is used during pregnancy to check your baby's risk of birth defects and genetic disorders, such as neural tube defects or Down syndrome. This information helps you and your health care provider decide if you need to have other tests to learn more about your baby's health.

AFP tests are often done as part of a group of prenatal tests, including:

• A multiple marker test, also called a triple screen
• A quad screen

Why do I need an AFP test?

An AFP test is routinely offered, usually between week 15 and 20 of your pregnancy. Your provider may especially recommend the test if your risk for having a baby with a birth defect or a genetic disorder is higher than usual because you:

• Have a family history of birth defects
• Are 35 years or older
• Have diabetes
• Have used certain medicines or drugs during pregnancy that could harm your baby

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 bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

The results of your AFP test tell you whether your baby is more or less likely to have certain birth defects and genetic disorders. The test can't diagnose any conditions.

Normal AFP test results mean that it's unlikely that your baby has a problem. But it's possible for a test result to be normal and miss a problem that does exist.

Abnormal AFP results may be a sign that your baby has a problem:

• Lower than normal AFP levels may mean your baby has an increased risk of a genetic disorder such as Down syndrome or Edwards syndrome.
• Higher than normal AFP levels may mean your baby has an increased risk of:
  • A neural tube defect, such as:
    • Spina bifida, a condition in which the bones of the baby's spine don't close around part of the spinal cord. It often causes damage to the spinal cord and nerves.
    • Anencephaly, a condition in which most of the baby's brain and skull don't develop. Almost all babies with this condition die shortly after birth.
  • A defect in the abdomen (belly) or esophagus (the tube that carries food from the baby's mouth to the stomach).

Abnormal AFP results don't always mean that your baby has an increased risk of a serious problem. High or low AFP levels may be caused by:

• An incorrect due date. AFP levels rise and fall at set times during pregnancy as the baby develops. That means normal levels of AFP are different at different times of your pregnancy. If your due date is wrong, your AFP blood level may seem abnormal when it's just right for how far along you really are in your pregnancy.
• Being pregnant with more than one baby. Each baby makes AFP, so your AFP blood levels will be higher with two or more babies.
• A false positive result. This means that your AFP results show an increased risk of a problem when there's really nothing wrong with your baby.

If your AFP test results aren't normal, you will likely have more tests to help find out why. If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.