As experts in obstetrics and gynecology, Atlanta Women's Specialists believes that an informed patient is an empowered patient. So we have made patient education a top priority. Look here for your guide to the most accurate information available on- and offline.
The Benefits and Limitations of Alpha-fetoprotein Tests
All prospective parents would like to know that the fetus growing in the uterus is entirely normal. Unfortunately, nature is not perfect and there are no tests that can identify all of nature's errors. Some studies can provide a degree of reassurance regarding certain abnormalities, but sadly, we have found that patients may seek this reassurance without fully understanding the nature or significance of the test they request. Consequently, we see a lot of confusion about results, and, worse yet, we see some people requesting tests that may not be appropriate for them. This is especially true of the Alpha-fetoprotein (AFP) test and its enhanced variant, the AFP-PLUS.
First, it is important to discuss what the AFP-PLUS will not do. It will not tell you that your baby is abnormal, and it will not guarantee that your baby is normal. It will not function as a complete alternative to amniocentesis or chorionic villus sampling. It will not tell you whether your baby has Down's syndrome, Spina Bifida, a heart defect, a limb defect or any other difficulty.
To understand the value it does have, you must appreciate the principle of statistical screening tests. The AFP-Plus is a screening test. It examines the statistical risks for two unassociated problems: spina bifida related abnormalities (neural tube defects) and Down's syndrome. The AFP-Plus is an optional blood test drawn between 15 and 20 weeks after the last menstrual period. It examines the level of three substances circulating in the mother's blood stream. The lab then uses these measurements along with your age and the age of the fetus to assign a statistical risk. A statistical risk is assigned for the chance of your baby having a neural tube defect and Down's syndrome. Since all babies are at risk for these two problems, your risk, based on the blood analysis, is compared to the probability of Down's syndrome and general population. In other words, AFP-Plus acts as an "odds maker" for only two abnormalities.
A positive result does not mean that your baby has any problem at all. In fact, even in the presence of an irregular screen, the likelihood is still significant that your baby does not have either of these two problems. If the test determines that your odds for a neural tube defect are greater than one chance in one thousand, or for Down's syndrome greater than roughly one in two hundred seventy, you will be given the option of having further testing. Such testing might be a repeated blood test or an ultrasound exam. In some case an amniocentesis may be offered to assist in making a final diagnosis.
Some of your friends may discourage you from taking this test because they believe it is wrong a lot of the time. This is not true. The AFP-Plus test cannot be wrong because it will never say that your baby does or does not have a problem. This test will tell us what the chance is that your child will have one of the two conditions discussed previously. If the test result were to return one in fifty, this says that if we called fifty mothers with a similar result, we would expect, on average, one mother to have a baby with problems and the other forty-nine babies would be fine. But all fifty mothers would have received the same phone call. This is the best the AFP-Plus can do. It will never give a simple yes or no answer. Not everyone is comfortable receiving information in this fashion because many of our medical tests are "yes or no" tests.
Considering these facts, who should have an AFP-Plus test? This test is designed for mothers who wish to confirm their low potential for Down's syndrome and neural tube defects. While the AFP-Plus can offer some additional reassurance, it can in no way guarantee normalcy. Couples should consider how the information from this test will or will not be useful to them. Some couples would consider termination if an abnormality was confirmed. Some couples want advanced warning in order to prepare themselves for a child with an abnormality. Some couples believe the information will not be helpful to them.
As a practice, we do not believe this is a good or a bad test. We believe everyone should know that this optional test is available. We also believe everyone should consider whether the information derived from this test is information they would like to receive. In addition, any woman over the age of 35 or with a suspected family history of birth defects should seek genetic counseling and consider definitive prenatal diagnosis. The AFP-Plus should only be ordered in this situation after discussing the special risks in detail with a provider. Atlanta Women's Specialists is pleased to offer you the AFP-Plus test. Please remember, it may not be suitable for everybody. Moreover, you must consider the limitations of this test and the nature of a screening program. If you have any questions, feel free to ask one of our provider or registered nurses for further details. If you elect to have the test and we report an irregular result to you, please do not diagnose a problem: An irregular result only indicates the need for further evaluation.
