Alpha-Fetoprotein (AFP) Test

Why this test may be ordered

• Fulfill a routine offering during pregnancy (usually between 15 and 20 weeks).
• Especially recommended if you have a family history of birth defects, are 35 years or older, have diabetes, or have used certain medicines or drugs during pregnancy that could harm your baby.

Preparation and collection

No special preparation is needed.

blood draw from a vein in the arm

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.

Understanding results

The AFP test measures the level of alpha-fetoprotein in your blood during pregnancy. It is a screening test that estimates your baby's risk of certain birth defects and genetic disorders. The test cannot diagnose any condition. Interpretation should be done by your healthcare provider, as AFP levels vary by gestational age and other factors.

• Screen-negative (lower-likelihood): Normal AFP levels are associated with a lower likelihood of neural tube defects, Down syndrome, or Edwards syndrome. Limitation: A normal result does not guarantee that your baby has no problems; false negatives are possible. Next step: If your AFP test results are normal, no further testing is usually needed unless you have other risk factors.
• Screen-positive (higher-likelihood): Lower than normal AFP may indicate an increased risk of Down syndrome or Edwards syndrome. Higher than normal AFP may indicate an increased risk of neural tube defects (e.g., spina bifida, anencephaly) or abdominal/esophageal defects. Limitation: An abnormal result may be a false positive and does not confirm a problem. It can also be caused by an incorrect due date, multiple pregnancy, or other factors. Next step: If your AFP test results are abnormal, you will likely have more tests (such as an ultrasound or amniocentesis) to help find out why.

• The AFP test is a screening test and does not diagnose any health conditions.
• A normal result does not rule out the possibility of a birth defect or genetic disorder (false negative possible).
• An abnormal result may be a false positive and does not confirm a problem.
• AFP levels vary with gestational age; an incorrect due date can lead to abnormal results.
• Abnormal results may cause emotional distress and require additional testing.

What to do next

If results are abnormal, follow-up tests such as ultrasound or amniocentesis may be recommended.

• What is an alpha-fetoprotein (AFP) test?
• Why do I need an AFP test?
• What happens during an AFP test?
• Will I need to do anything to prepare for the test?
• Are there any risks to the test? What do the results mean?

Evidence source

U.S. National Library of Medicine: Alpha-Fetoprotein (AFP) Test