Maternal Serum Alpha-Fetoprotein (MSAFP)
Alpha-fetoprotein (AFP) is a protein that is produced by the fetus' liver. A small amount crosses the placenta and moves into the mother's blood stream. As the baby grows and produces more AFP, the amount in the mother's blood increases.
Between weeks 15 and 20 of a pregnancy, a maternal serum alpha-fetoprotein (MSAFP) screen will be offered, usually as part of a test known as a triple screen, enhanced AFP, or multiple marker screen (MMS). The test determines how much AFP is in the blood, and also measures the levels of two pregnancy hormones, estriol and human chorionic gonadotropin (hCG).
The quantity of AFP that is considered normal depends upon many variables, including age, weight, race, and stage of pregnancy. Insulin-dependent diabetes also influences AFP levels. Of those women whose tests show high or low levels of AFP, only two or three in 100 will have a child with a birth defect.
This test is offered to all pregnant women. You may choose to have this test if you want to know if your baby is at high risk for certain birth defects. You may want to take an MSAFP test before considering ultrasound, chorionic villus sampling (CVS), or amniocentesis.
What Will Happen?
An MSAFP screen involves a simple blood draw. In general, a nurse or lab technician cleans the skin on the inside of the elbow with antiseptic. A tourniquet is then tightly wrapped around the top of the arm to restrict blood flow, allowing the vein to stick out. A quick prick may be felt as a thin, hollow needle is inserted into the vein. Once the needle is in place, blood is withdrawn into an airtight vial or a syringe. During the procedure, the tourniquet will be removed to restore blood flow. Once the sample is collected, the needle is removed and the puncture site is dressed with a bandage.
Results are usually available in one week. Up to 10% of results are positive, meaning you have high- or low-AFP levels. With a positive AFP, additional tests will be suggested to help determine the cause.
Follow-Up Tests May Include:
- A repeat MSAFP screening if the age of the fetus has been re-evaluated by an ultrasound.
- Ultrasound to more precisely pinpoint the age of the fetus or detect multiple fetuses.
- A high-resolution ultrasound to get a sharper view of the fetal skull, spine, and other organs to detect or rule out neural tube defects (this test, however, is not widely available).
- Genetic counseling.
- Amniocentesis, which assesses the AFP level in the amniotic fluid and analyzes fetal cells to detect or rule out certain birth defects (such as Down syndrome).
Positive AFP levels are most often the result of a miscalculation in the age of the fetus or multiple fetuses in the womb, with each producing AFP. In some instances, the reason for a positive AFP level remains unknown. Only a small number of positive results (between 0.02% and 0.03%) are related to a birth defect. Unusually high AFP levels are associated with an increased risk of a neural tube defect such as spina bifida or anencephaly, whereas unusually low levels (along with low levels of estriol and high levels of hCG) are related to an increased risk of a chromosomal abnormality such as Down syndrome. Even more rare is when high AFP levels suggest the fetus is dying or dead.
It's important to remember that an MSAFP is a screening test only; it does not detect or diagnose birth defects. The majority of women who take this test receive normal, or negative, results.
Frequently Asked Questions
Q: What are some of the benefits and risks of having this test?
A: A potential benefit is that the screening results may warrant additional testing that could lead to the early detection of a developmental abnormality in the fetus. Early identification of any problem allows you and your health-care team crucial time to explore treatment options, ensuring the utmost safety of your pregnancy and delivery. With normal test results, you may benefit from the assurance that your baby does not appear to be at high risk for certain abnormalities. On the other hand, if the test reveals a positive AFP result, you risk experiencing anxiety as well as more invasive testing to determine the cause, even though most of the time the positive results do not indicate a birth defect.
Q: Does AFP show up in the blood when you're not pregnant?
A: In some cases, AFP is found in the blood of people who have hepatitis, liver cancer, and certain types of ovarian or testicular cancer. It is also found in the blood of children and adolescents who have pineal gland tumors.
Review Date: June 29, 2001
Reviewed By: Peter Chen, M.D., Obstetrics and Gynecology, University of
Pennsylvania School of Medicine. Review provided by VeriMed Healthcare
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