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Alpha-Fetoprotein Screening

What is alpha-fetoprotein screening?

Alpha-fetoprotein or AFP screening is a blood test for pregnant women, which is most commonly ordered in the second trimester around 16 weeks. It can be used to look for a problem in the baby's spine or other conditions, such as certain birth defects.

The test measures the level of a protein called alpha-fetoprotein (AFP) in your blood. It is a way to check for some types of birth defects.

AFP is a protein and is normally produced 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 a birth defect. 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 elevated AFP can indicate a higher chance of having other problems later in the pregnancy, such as:

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

A very low level of the protein can sometimes be seen with Down syndrome, but other tests are usually performed for this genetic problem.

Other possible causes for abnormal 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 test is usually done between the 15th and 18th weeks of pregnancy. The blood is collected in tubes and sent to a lab.

It is important to have the test at the right time in your pregnancy. If the AFP level is higher or lower than normal, enough time must remain in your pregnancy for further steps. These steps might include ultrasound and counseling. Also, for the test to be interpreted properly, you and your healthcare provider need to be sure of your due date.

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 AFP levels are normal. Or a baby may be quite normal even though AFP levels are abnormal. Usually, if the first blood test shows normal levels, no further special tests are done. If the first test shows abnormal levels of AFP, it may be repeated before other tests are done.

For every 1000 pregnant women tested, about 50 have abnormal test results. Of these 50, just 1 or 2 with high AFP levels have babies with problems. The test finds 90% of babies with anencephaly and 75% with spina bifida.

A test called a triple or quad screen has been developed to provide more accurate screening for birth defects. In addition to AFP, your blood is tested for 2 or 3 other substances produced by the placenta. 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 a wider variety of 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 determine 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 that your baby probably does not have a serious defect.

Abnormal results can help you and your healthcare provider manage your pregnancy better. Pregnancy care is sometimes changed by your healthcare providers to allow them to monitor 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 these defects. This may improve the outlook for your baby.

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.