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Alpha-Fetoprotein (Maternal Blood)

Does this test have other names?

msAFP screen

What is this test?

If you are pregnant, this test looks for a fetal substance called alpha-fetoprotein (AFP) in your blood.

AFP is a protein made by your fetus' liver. The protein passes through the placenta and into your blood. The test helps find out whether your fetus has higher than normal levels of AFP.

Higher levels of AFP may mean that your fetus has an abnormality such as a neural tube defect. An example is spina bifida. Neural tube defects are serious birth defects in which the spinal cord and brain don't properly develop. If a fetus has this defect, it will probably have an opening in the head, spine, or stomach wall that causes high levels of AFP to travel into the mother's blood.

Lower levels of AFP may mean that your fetus has Down syndrome. Down syndrome is an abnormality involving an extra chromosome (chromosome 21).

Why do I need this test?

If you are pregnant, your healthcare provider will offer this test to look at AFP levels in your blood and find out your fetus' health. You may have this test during weeks 15 to 20 of your pregnancy. You may have this test to see whether your fetus has signs of Down syndrome or other birth defects.

What other tests might I have along with this test?

Your healthcare provider may also order blood tests to help make an accurate diagnosis. These tests include:

  • hCG

  • Unconjugated estriol

  • Inhibin A

You may have the following tests if your msAFP results are positive:

  • Ultrasound

  • Amniocentesis, which looks at the fluid around your fetus

  • Noninvasive prenatal screening, which is a blood test in the mother to check if the baby could have a chromosome abnormality (Down syndrome, trisomy 13, trisomy 18, etc.)

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

Results are given in nanograms per milliliter (ng/mL). Here is the normal range:

  • For adults: less than 40 ng/mL

  • At 15 to 21 weeks' gestation: 10 to 150 ng/mL

AFP levels typically rise until around the 12th week of pregnancy. Then the levels drop consistently until birth.

If your fetus has Down syndrome, substances like AFP and unconjugated estriol will likely be low. But hCG and inhibin A levels will probably be high.

If you have a positive test result, it does not mean that your fetus definitely has a defect. Most pregnant mothers who test positive are actually carrying a healthy fetus. A positive test result may mean additional testing is needed, such as an amniocentesis.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

If you have recently been given a screening test for embryonic teratocarcinoma or hepatoblastoma, a liver tumor, your AFP levels may be higher than normal.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.

Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Maryann Foley RN BSN
Online Medical Reviewer: Raymond Turley Jr PA-C
Date Last Reviewed: 3/1/2022
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