What Can an AFP Test Tell You About Your Baby?

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When you’re pregnant, there are a variety of tests that are offered at different points throughout your prenatal care. These are generally screening tests, as opposed to diagnostic tests. What’s the difference between the two? Screening tests are generally given to a wide variety of people, including asymptomatic people, to look for early diseases or problems, or to identify any possible risk factors for a condition.

A diagnostic test determines whether a condition is present. A diagnostic test is more definitive with 100 percent accuracy, whereas a screening test has a wide margin of error and is typically used as a precursor to diagnostic tests if need be.

What Is an AFP Test?

One of the screening tests that is typically done during pregnancy is the alpha-fetoprotein (AFP) test, also called the maternal serum alpha-fetoprotein (MSAFP) test. It’s generally done as part of the triple screen test, which also contains an hCG test and estriol test, and helps to screen for possible birth defects. The triple screen is most accurate if it’s done between the 16th and 18th weeks of pregnancy, but can be done anywhere between 15 and 22 weeks of pregnancy. If there are any abnormal results in the screening tests, further testing and follow up are performed.

The AFP test is a simple blood test that measures the amount of alpha-fetoprotein in your blood.

While the exact function of AFP is unknown, it is made by the fetal liver, and the level of AFP rises and falls at specific times in the pregnancy. High levels of AFP—when it should be lower—might indicate genetic disorders or conditions, including spina bifida, anencephaly, certain structural defects, or chromosomal abnormalities like Down syndrome.

However, because it’s merely a screening test, it can’t tell you what exactly is going on, or whether the fetus definitely has any of these issues. Diagnostic tests would be needed for more definitive answers. There are also false-positives, which are often the result of pregnancy dating being inaccurate. If you’re having multiples, this also affects the AFP screening.

What Happens in an AFP Test?

The AFP test is a simple blood test where blood is drawn from a vein and sent to a lab. Results usually take two weeks or less. Since the timing of this test is crucial, it is usually done between the 15th and 20th weeks of pregnancy. Because it’s just a regular blood draw, there are no risks to you, besides the general blood test risks (i.e., soreness at injection site, bruising), or to your fetus.

If the AFP test comes back showing elevated levels, you might need another AFP, along with a high definition ultrasound. These will make sure the dating of the pregnancy is correct, and look at fetal structures like the skull and spine. If there are still any uncertainties or causes for concern, your doctor or midwife might suggest a more invasive diagnostic test like an amniocentesis.

You do have the option to decline further testing; that is your choice.

Some people find it helpful to have as much information as possible in order to think about potential medical interventions, seek out support groups or resources, and be able to plan for a child with special needs. Some people want to know the information in order to make a decision about whether or not to carry the fetus to term. Other people decide to wait until the baby is born to deal with these issues, should they be necessary—and that’s okay.

A Word From Verywell

If you’re nervous about the AFP, or if the screening test came back and warrants further follow up, talk with your healthcare provider.

If you have a partner, talk with them about your feelings regarding any possible AFP results, what that might mean, and how it will affect you. It’s important to remember that the AFP test is not diagnostic, and isn’t perfect. It can be helpful to be informed, but know that the results aren’t always accurate. Your healthcare provider can tell you more about the test, how it helps inform further diagnostic testing, and any risks that further testing might entail.

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