An AFP (alpha-fetoprotein) test is a simple blood test. It can show whether your fetus has signs of some birth defects. This test is done between weeks 15 and 20 of pregnancy.
You'll get your AFP test results within
Most AFP results are negative (normal). This means the test results show no signs of the birth defects tested for. Sometimes results are positive (abnormal). Often, this is simply because:
Your due date is different than first thought.
You have twins.
Some positive results show that the fetus may have one of the following birth defects:
Neural tube defects (problems with the spine, such as spina bifida)
Abdominal wall defects (problems with the body of the fetus)
Genetic defects (physical or mental problems, such as Down syndrome)
While it happens rarely, AFP test results can be wrong. These are called false negatives or false positives. Be sure to ask your healthcare provider any questions you have about your results.
An AFP test is only a screening test. The most it can do is point to a possible problem. If your results point to a problem, other tests will be needed to confirm the results. Keep in mind that most AFP test results are normal. Even when they're not, the results of the follow-up tests most often are.