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Re: nuchal translucencyFrom: James S Smeltzer MD (gaperina@mindspring.com)Tue Aug 4 18:34:36 1998
Tania, The triple test is a maternal blood test. Amniocentesis is done to perform a test of fetal cells from the fluid around the baby. The accuracy of amniocentesis is at least 99+% for Downs & other major trisomies, because it is. THis is the probability that amniotic fluid sent to reputable lab will yield (after cell culture, harvesting in metaphase arrest, appropriate staining, counting & photography and assembly of a karyotype, interpretation & reporting) a report that reflects the actual chromosomal complement of a large majority of the cells of a particular baby. This is the gold standard test. It is almost as certain as death and taxes. If it were done on every pregnant woman, few chromosomal anomalies would occur not detected before birth. The large majority of the two percent of babies with major anomalies would not be detected by this method, however. The problem is that not every pregnant woman gets this test. Selection based on age means that about a third could be detected by testing 20 percent of the pregnant population, and about one normal baby in 1200 is killed by the testing. Based on triple screen and age, about 70% are detected by testing about 25% of the pregnant population, and only one normal baby in a thousand is killed by the testing. The big deal about nuchal edema is this: based on nuchal edema and age about 80% are detected by testing 5% of the population, and one normal baby in 5000 is killed by testing. This is a lot better than any other system we've had. The expense of the test can be reduced substantially by screening all samples for the right number of the sex and major live anomaly chromosomes (13, 18, 21) by something called FISH, which does not use such an elaborate procedure, but DOES correctly identify 99.9% of the problems (abnormal numbers of chromosomes) the risk that indicates the amniocentesis test for the large majority of women who get the test. The other "abnormalities" found can not usually be classified as bad, with predictable severe adverse consequences. When we find them we usually worry and confuse parents as much as we help them. The risk of loss of a normal fetus related to this procedure is certainly a major factor, being about 1/200 to 1/500, so it would not ever make sense to do genetic testing on everyone, even if free, unless fetal cells can be obtained without risk and major expense. People are working on how to do this from mother's blood. There are problems of finding enough of these cells, cells from prior pregnancies (and even vanished twins) hanging around and other technical details to be ironed out. Finding all chromosomal anomalies is only a third of all anomalies, even then. Some people who do ultrasound have enough experience and practice and interest to think they can find AT LEAST two thirds of major life-threatening anomalies with a single ultrasound, which is more than even a 100% detection of chromosomal anomalies. Others have found that experience counts, but they find only about a third. One potential adverse effect of universal early ultrasound for nuchal thickening is that it could reduce the number of babies looked at carefully by experts for chromosomal problems, in lieu of amniocentesis, and the other serious problems detected by these experts, too (and the income of these experts). Perhaps the greatest benefit of universal first trimester sonography is the establishment of virtual certainty of pregnancy dates for these patients. Since the treatment of almost every complication of obstetrics is different at different gestational ages and accurate detection of a major problem, abnormal growth, depends on knowing gestational age, many babies can be potentially saved, and many other babies and their mothers spared unnecessary and potentially dangerous treatment, by this practice. Stuart Campbell showed that routine early sonographic dating could eliminate two thirds of the babies who were identified as being inside too long - and thus subject to induction of labor. A more radical question is whether or not it is really beneficial to identify and destroy all babies with Down's Syndrome, even if we could. I do not believe this is true, and I think that most of the people with Down's Syndrome would agree with me. The majority of those with the more severe extra chromosomal anomalies (13 and 18), can be detected by routine sonography. While some of their parents may disagree, none of these will dispute the statement that they would suffer less by not being born, as they can not talk. These are difficult issues, as they cut to the core of who we are, why we are here and what life is all about. It is certainly NOT about living happily ever after in a world without problems - although it may be something about creating such a world by how we help others with their problems, and learn to face our own with courage, humility and a desire for understanding and change. If you have more specific questions about what I said, please ask. There are good books on the subject out there. Jim Smeltzer MD (gaperina@mindspring.com)
At 04:43 PM 8/4/1998 -0500, you wrote:
>still a bit confused.
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