AFP Test: What Does It Show?

I am almost 20 weeks pregnant with my third child. My second child was born with a club foot and syndactylus toes and almost had spina bifida. My husband and I are very nervous about this next child, so my doctor ordered alpha-fetoprotein testing. What does this test measure and will it show if my baby is healthy and complete?

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ABOUT THE EXPERT

Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

I would highly recommend the services of a genetic counselor if one is available in your area. Genetic counselors are highly trained professionals who take a complete family history, look at any studies done to date, educate you about risks and recommend what tests should be done, if any. They can usually be found at large medical centers or in university settings.

I am glad you are considering an AFP test. It will measure your risk of having a baby with an open spinal defect such as spina bifida. It is not, however, a perfect test. It is only a screening test, and false high and low levels do occur. If the level seems high or low, the counselor should encourage an ultrasound and amniocentesis.

It is best to do the initial AFP on your blood, so there is no risk to the baby. This initial test should be done between 15 and 20 weeks. Falsely high values may result if the mother has diabetes or is pregnant with twins. Only about 5 percent of women will have an elevated blood level. About one in 15 women with an unexplained elevated AFP will have a fetus with a neural tube defect. Low levels of AFP are associated with an increased risk for Down syndrome.

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