What Is AFP, or Alpha-Fetoprotein?

By Bailey Miller
Reviewed by Alyssa Quimby, M.D.
June 06, 2024

AFP (alpha-fetoprotein) is a protein the fetus naturally produces in the liver during pregnancy. Your doctor will recommend doing routine testing to determine the level of this protein in your blood between weeks 15 and 20 of pregnancy (in the second trimester).

A level that’s higher or lower than typical could be a sign of several things, including a neural tube defect or Down syndrome. It could also mean your due date was estimated incorrectly or that you’re carrying twins.

AFP levels vary naturally throughout pregnancy, and an AFP test is not diagnostic. That means that an abnormal result doesn’t necessarily mean there’s a problem. If the AFP test result is outside typical range, your doctor will likely recommend additional testing to find out why.