Alpha-fetoprotein (AFP) is a protein produced in the liver of a developing fetus. During a baby's development, some AFP passes through the placenta and into the mother's blood. An AFP test measures the level of AFP in pregnant women during the second trimester of pregnancy. Too much or too little AFP in a mother's blood may be sign of a birth defect or other condition. These include:

• A neural tube defect, a serious condition that causes abnormal development of a developing baby's brain and/or spine
• Down syndrome, a genetic disorder that causes intellectual disabilities and developmental delays
• Twins or multiple births, because more than one baby is producing AFP
• Miscalculation of due date, because AFP levels change during pregnancy

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

The American Pregnancy Association says that all pregnant women should be offered an AFP test sometime between the 15th and 20th week of pregnancy. The test may be especially recommended if you:

• Have a family history of birth defects
• Are 35 years or older
• Have diabetes

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. Another test called amniocentesis provides a more accurate diagnosis of Down syndrome and other birth defects, but the test has a small risk of causing a miscarriage.

If your results show higher than normal AFP levels, it may mean your baby has a neural tube defect such as spina bifida, a condition in which the bones of the spine don't close around the spinal cord, or anencephaly, a condition in which the brain does not develop properly.

If your results show lower than normal AFP levels, it may mean your baby has a genetic disorder such as Down syndrome, a condition that causes intellectual and developmental problems.

If your AFP levels are not normal, it doesn't necessarily mean there is a problem with your baby. It may mean you are having more than one baby or that your due date is wrong. You may also get a false-positive result. That means your results show a problem, but your baby is healthy. If your results show a higher or lower than normal level of AFP, you will likely get more tests to help make a diagnosis.

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