What is an alpha-fetoprotein (AFP) screening test?

Alpha-fetoprotein screening is a blood test that checks the level of alpha-fetoprotein in the mothers' blood during pregnancy. AFP is a protein normally made by the baby’s liver. It is found in the fluid surrounding the baby in the womb (amniotic fluid). AFP goes through the placenta into the mother's blood. The AFP blood test is called MSAFP (maternal serum AFP). The AFP can also be measured in the amniotic fluid, called AFAFP.

Too much or too little AFP may be a sign of:

• Open neural tube defects (ONTD), such as spina bifida

• Down syndrome

• Other chromosomal abnormalities

• Defects in the abdominal wall of the baby

• Twins (more than 1 baby is making the protein)

• A miscalculated due date, as the levels change during pregnancy

You may have an AFP test as 1 part of a 2-, 3-, or 4-part screening. This is sometimes called a multiple marker screen. The other parts of the test may check for:

• hCG (Human chorionic gonadotropin hormone). This is a hormone made by the placenta.

• Estriol. This hormone is made by the placenta.

• Inhibin-A. This is a hormone made by the placenta.

Abnormal test results for AFP and other markers may show a need for more testing. An ultrasound can usually confirm the dates of the pregnancy. It is also used to look at the baby’s spine and other body parts for defects. An amniocentesis may be needed for accurate diagnosis.

How is an alpha-fetoprotein screening test done?

In most cases, an alpha-fetoprotein test is done this way:

• Blood is usually taken from a vein between the 15th and 20th weeks of pregnancy.

• The blood sample is then sent off to be checked at a lab.

• Results of the tests are usually ready in 1 to 2 weeks or less, depending on the lab.

What are the risks and benefits of an alpha-fetoprotein screening test?