The AlphaFetoprotein test is a blood test which must be carried out between 15-18 weeks gestation. Alpha Fetoprotein is a protein produced by the fetal liver. It's presence in the blood is primarily used to detect neural tube defects such as spina bifida, but it is also used to screen for Down's Syndrome and other conditions.
This is a simple blood test, so the risk is not in the actual test but in the results. Out of 1000 women tested, 50 will have an abnormal reading, but only 1 will actually have an abnormality. The remaining 49 will have false positive tests. If you are one of those other women, you are led to believe that your baby has a defect when it doesn't. This causes a lot of unnecessary anxiety, and while it might be nice to know in advance if your baby has a defect, there is nothing that can be done to correct it before birth, and your prenatal care will be the same.
The test accurately identifies only 70% of open neural tube defects, 10% of closed neural tube defects, and 10-20% of Down's Syndrome babies. The test MISSES 10% of anencephaly cases, 40% of spina bifida, and almost 80% of Down's Syndrome cases.*
By the way, 80% of Down Syndrome babies are born to women UNDER 35 years of age.
Alpha Fetoprotein must be tested PRECISELY between 15 and 18 weeks in order for it to be accurate, so it has questionable value for those who are not sure of their dates.
Things that can cause a false positive reading are:*
Taking drugs such as aspirin, acetaminophen, erythromycin, insulin, propanalol, or methyldopa.
Twins, threatened abortion, inaccurate dates, low birth weight, a sample contaminated with fetal blood, liver disease, and alcoholism can all raise levels. Falsely low readings can be due to a female fetus or diabetes. Of course, chromosomal abnormalities like Down's Syndrome, as well as molar pregnancy also are associated with low levels, but the majority of the time this is not the case.
Other less common reasons for a positive result are: congenital Finnish nephrosis, Turner syndrome with cystic hygromas, gastrointestinal obstructions, missed abortion, imminent or actual fetal demise, severe Rh problems, and esophageal or duodenal atresia, skin defects and other conditions associated with fetal edema.
In many cases, the test is offered so that abortion can be offered to those women whose tests come back positive. I personally know of instances where babies were aborted and found to be perfectly healthy with no defects. These mothers were heartbroken that they allowed a healthy baby to be killed.
If you do choose to have the AFP test, I strongly encourage you to ask for the triple screen with interpretations. In this test, your blood is checked for levels of AFP as well as two other hormones which can give a more accurate reading than just AFP alone.
Remember, the risk of losing a baby from more invasive tests is greater than having a baby with the problem in question. In other words, if you have a positive AFP, you will be asked to undergo amniocentesis or chorionic villus sampling. The risk of miscarriage from these procedures is, for for many women, higher than the actual risk of having a baby with a neural tube defect or chromosomal abnormality. In short, it isn't worth the risk.
*Statistics taken from "Understanding Diagnostic Tests in the Childbearing Year", 6th edition, by Anne Frye, 1997, p. 728.
*Conditions associated with false readings are taken from "Understanding Diagnostic Tests in the Childbearing Year", 6th edition, by Anne Frye, 1997, p. 729.
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