Healthy Pregnancy

What is the alfa-feto protein screen?

The Alpha-Feto Protein (AFP) Screen is a blood test to screen for neural tube and chromosomal abnormalities. It has a high incidence of false positives which is normal for many screening tests — with screening tests it is important to know who does NOT need more extensive testing.  It is possible, but much more rare, to a false negative.

AFP is produced by your baby’s liver, is present in your baby’s blood and transfers to your blood thorugh the placenta. Your blood will be screened to determine the amount of AFP. As your baby grows, the level of AFP rises, so for accuracy it is important to know how old the baby is. This screening test is most accurate between 16 – 18 weeks pregnancy.

If the AFP is “high” it can mean:

  • Multiple pregnancy
  • Open neural tube defect such as Spina Bifida (AFP is able to leak out the opening of the neural tube which causes higher than normal levels in your blood)
  • Baby is older than you thought

If the AFP is “low” it can mean:

  • Down Syndrome (about 1/5 of babies with down syndrome are detected with AFP)
  • Baby is younger than you thought
  • Insulin dependant diabetics have a decreased level of AFP, so be sure your health care team knows your health history

Because this is a screening test, a positive finding only indicates the possibility of a problem. Further testing will be necessary to determine if your baby is having a problem. 98% of women who receive positive results turn out to have healthy babies.

If spina bifida is confirmed through further testing, you will have the opportunity to give birth via cesarean surgery to prevent compression of the spinal cord. However, spinal defects are rare, only one or two per 1000 babies. Many babies with spinal defects miscarry.

If your test comes back high your choices will be to:

  • Repeat the test and compare the results
  • Use ultrasound to examine the baby. Ultrasound can see some neural tube defects, check age and check for twins
  • Use amniocentesis to help further determine health of baby

If your test comes back low your choices will be to:

  • Use ultrasound to examine the baby. Ultrasound can help to check age and undetected miscarriage.
  • Test for maternal diabetes
  • Amniocentesis to help further determine health of baby
Jennifer (Author)