What is an Alpha-fetoprotein (AFP) Test?
An AFP test is a test that is mainly used to measure the level of alpha-fetoprotein (AFP) in the blood of a pregnant person. The test checks the baby's risk for having certain genetic problems and birth defects. An AFP test is usually done between 15 and 20 weeks of pregnancy.
AFP is a protein that a developing baby makes. Normally, some AFP passes from the baby into the pregnant person's blood. Certain conditions can make a baby's body release more or less AFP. During pregnancy, if your AFP blood levels are higher or lower than normal, it may be sign that:
- The baby has a high risk of having a genetic disorder, such as:
- Your estimated due date is wrong. AFP levels normally rise and fall at set times during pregnancy, so an abnormal AFP may mean that your baby is due earlier or later than estimated. This is the most common reason for abnormal AFP levels.
- You're pregnant with more than one baby. Each baby makes AFP, so your AFP blood levels will be higher with two or more babies.
Other names: AFP Maternal; Maternal Serum AFP; msAFP screen
What is it used for?
An AFP blood test is used during pregnancy to check the baby's risk of birth defects and genetic disorders, such as neural tube defects or Down syndrome. The test does not diagnose any health conditions. If your AFP test results aren't normal, it means you need more testing to find out whether your baby has a health problem.
For people who aren't pregnant, an AFP test may be used to help diagnose certain cancers that may cause high AFP levels in adults. When the test is used this way, it's called an AFP tumor marker test.
Why do I need an AFP test?
If you are pregnant, AFP test is routinely offered between the 15th and 20th week of pregnancy. Your provider may especially recommend the test if you:
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 most common cause for abnormal AFP test results during pregnancy is an error estimating your due date. But a result that isn't normal may also be a sign of possible problems:
- Lower than normal AFP levels may mean your baby has a genetic disorder such as Down syndrome, a genetic disorder that causes intellectual disabilities and health problems.
- Higher than normal AFP levels may mean your baby has an increased risk of having a neural tube defect, such as:
High AFP levels may also mean that you are having more than one baby. You may also get a false-positive result. That means that your AFP results aren't normal, but your baby is healthy.
If your AFP test results aren't normal, you will likely have more tests to help make a diagnosis.
Learn more about laboratory tests, reference ranges, and understanding results.
Is there anything else I need to know about an AFP test?
AFP tests are often part of a group of prenatal tests called multiple marker or triple screen tests. These tests can help diagnose Down syndrome, trisomy 18 (Edwards syndrome), and other genetic disorders. A triple screen test includes tests for:
- Alpha-fetoprotein (AFP)
- Human chorionic gonadotropin (HCG), a hormone produced by the placenta
- Estriol, a form of estrogen made by the baby and the placenta
In some cases, a fourth test is included, called an inhibin A test, which helps diagnose Down syndrome.
If you have a high risk for having a baby with certain birth defects, your provider may also recommend a test called prenatal cell-free DNA (cfDNA) screening. This is blood test can be done 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.
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