Alpha-Fetoprotein (Maternal Blood)

msAFP screen

If you are pregnant, this test looks for a fetal substance called alpha-fetoprotein (AFP) in your blood.

AFP is a protein made by your fetus' liver. The protein passes through the placenta and into your blood. The test helps find out whether your fetus has higher than normal levels of AFP.

Higher levels of AFP may mean that your fetus has an abnormality such as a neural tube defect. An example is spina bifida. Neural tube defects are serious birth defects in which the spinal cord and brain don't properly develop. If a fetus has this defect, it will probably have an opening in the head, spine, or stomach wall that causes high levels of AFP to travel into the mother's blood.

Lower levels of AFP may mean that your fetus has Down syndrome. Down syndrome is an abnormality involving an extra chromosome (chromosome 21).

If you are pregnant, your healthcare provider will offer this test to look at AFP levels in your blood and find out your fetus' health. You may have this test during weeks 15 to 20 of your pregnancy. You may have this test to see whether your fetus has signs of Down syndrome or other birth defects.

Your healthcare provider may also order blood tests to help make an accurate diagnosis. These tests include:

• hCG

• Unconjugated estriol

• Inhibin A

You may have the following tests if your msAFP results are positive:

• Ultrasound

• Amniocentesis, which looks at the fluid around your fetus

• Noninvasive prenatal screening, which is a blood test in the mother to check if the baby could have a chromosome abnormality (Down syndrome, trisomy 13, trisomy 18, etc.)

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Results are given in nanograms per milliliter (ng/mL). Here is the normal range:

• For adults: less than 40 ng/mL

• At 15 to 21 weeks' gestation: 10 to 150 ng/mL

AFP levels typically rise until around the 12th week of pregnancy. Then the levels drop consistently until birth.

If your fetus has Down syndrome, substances like AFP and unconjugated estriol will likely be low. But hCG and inhibin A levels will probably be high.

If you have a positive test result, it does not mean that your fetus definitely has a defect. Most pregnant mothers who test positive are actually carrying a healthy fetus. A positive test result may mean additional testing is needed, such as an amniocentesis.

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

If you have recently been given a screening test for embryonic teratocarcinoma or hepatoblastoma, a liver tumor, your AFP levels may be higher than normal.

You don't need to prepare for this test. But be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.