Alpha-Fetoprotein Screening

What is alpha-fetoprotein screening?

Alpha-fetoprotein or AFP screening is a blood test for pregnant women. The test measures the level of a protein called alpha-fetoprotein (AFP) in your blood. It can be used to look for a problem in the baby's spine or other conditions, such as some types of birth defects. It is done in the second trimester of pregnancy between 14 and 23 weeks. It is usually done around 16 weeks.

AFP is a protein normally made by your baby in relatively high amounts. Some AFP passes from the baby into your bloodstream. If a baby has certain problems, the level of AFP may be unusually high or low. However, most of the time when the AFP levels are abnormal, the baby is fine. Because the test is not completely accurate, your healthcare provider will usually order other tests if the AFP levels are high or low.

What problems does the test find?

A high level of AFP may indicate that the baby has a higher chance of having certain birth defects. Examples of problems that can cause a high AFP are:

• spina bifida (the spine has not closed normally)
• kidney problems
• severe skin problems
• severe chromosome problems (other than Down syndrome)
• anencephaly (all or part of the brain is missing)
• a failure of the front of your baby's abdominal wall to close completely, so that the intestines are enclosed in a sac or are exposed to the amniotic fluid around the baby
• a defect in the esophagus (food pipe)

Even if the baby does not have a birth defect, a very high AFP can indicate a greater chance of other problems later in the pregnancy, such as:

• intrauterine growth restriction (IUGR) and low birth weight
• oligohydramnios (too little amniotic fluid)
• preeclampsia (very high blood pressure and swelling)
• the placenta pulling away from the inside wall of the uterus
• death of the baby

A very low level of AFP is sometimes seen with Down syndrome, but other tests are usually done for this genetic problem.

Other possible causes of abnormal AFP levels are:

• an incorrect due date
• the presence of more than 1 baby
• miscarriage
• a baby who is smaller than normal
• an overweight mother, especially if the mother is African American
• diabetic mother

How is the test done?

A small amount of blood is taken from your arm with a needle. The blood is collected in tubes and sent to a lab.

How will I get the test results?

Ask your healthcare provider when and how you will get the result of your test.

How accurate is the test?

The test is not completely accurate. A baby may have a birth defect even with normal AFP levels. Or a baby may be quite normal even though AFP levels are not normal. Usually, if the first blood test shows normal levels, no further special tests are done. If the first test shows abnormal levels of AFP, then other tests are done.

For every 1000 pregnant women tested, about 50 may have abnormal test results. Of these 50, just 1 or 2 with high AFP levels have babies with problems. The test can find most babies with nervous system problems called anencephaly or spina bifida.

The test is usually done between the 15th and 18th weeks of pregnancy. For the test to be interpreted properly, you and your healthcare provider need to be sure of your due date.

A test called a triple or quad screen has been developed to provide more accurate screening for birth defects. When you have one of these tests, your blood is tested for 2 or 3 other substances produced by the placenta as well as AFP. These substances are human chorionic gonadotropin (hCG), unconjugated estradiol (uE), and dimeric inhibin-A (DIA). These combination tests are used to help detect pregnancies that have a higher chance of having problems.

What if the results are not normal?

Abnormal results indicate the need for further tests, such as:

• detailed ultrasound scans (a scan of your uterus and the baby with sound waves)
• amniocentesis (a test of the fluid around the baby) to look at the baby's chromosomes
• cordocentesis, or percutaneous umbilical blood sampling, which is a way to get cells from the baby's blood to test for chromosome problems

In some cases these tests find no reason for abnormal AFP results.

Talk to your healthcare provider about your results and ask questions. Ask if and when you need more tests. If the results of the AFP test and follow-up tests show that your baby does have a serious problem, your provider will talk to you about your choices of treatment.

What are the risks of AFP testing?

It is common to have feelings of anxiety when having tests to see if your baby might have a problem. However, there is virtually no risk to you or your baby from this test.

What are the benefits?

Most often, the test reassures you and your healthcare provider that your baby probably does not have a serious defect.

When the results are abnormal, the test can help you and your healthcare provider manage your pregnancy better. Your provider may watch the development of your baby more closely. Sometimes there are treatments or therapies that can be started during pregnancy that can help babies with a problem. Your provider may plan your delivery in a center equipped to deal with expected problems or help to make other plans for your baby after birth.

Your provider can offer you counseling to help you prepare for the baby's problems. There are also many support groups for families who have children with birth defects. You may find it helpful to get in touch with these groups before or after your baby is born.