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Re: Down Syndrome: New screening methods questionedFrom: viv souter (vsouter@yahoo.com)Tue Aug 13 19:22:03 2002
Hi This is not the first UK paper to decry screening for Down syndrome based on population screening results. I have only looked briefly at the paper but I am surprised the BMJ did not insist that the uptake rate for screening in each center was not made clear in the paper...... Viv Terry J DuBose wrote:Dr. Deigan, thanks for this good review of the article. This article seems to have problems similar to the RADIUS study in the USA ... Thanks again for this... hopefully we will have some good prospective studies soon... FASTER? Peace, Terry J DuBose, M.S., RDMSLittle Rock, Arkansas USA On Tue, 13 Aug 2002 06:57:38 -0500 "Dr. Eric Deigan" <ericdeigan@prodigy.net> writes: Terry, This article should not be used to judge the effectiveness of NT screening. I reviewed the original article, and yes, there are lots of problems in using it to assess the value of nuchal translucency screening. In fact, I also was able to find some evidence within this study to show that NT screening can work well! A quick summary of the problems: 1) Selective application of nuchal translucency (NT) screening to advanced maternal age women will lower the detection rate for Down syndrome in a population: This is probably the biggest problem in using this study to look at NT screening. Of the 3 districts who offered NT screening, one of them, which was also the district that had the most number of cases of Down syndrome in the study and far more than the other two that offered NT, generally offered it only to women age 34 or over, while the groups using invasive testing for maternal age alone were offering it to everyone 35 and over. If you offer nuchal translucency testing to women of advanced maternal age, you will actually lower the detection rate for Down syndrome. As a simple example -- if 100% of women age 35 or over have amnio, you detect 100% of the Down syndrome cases in that age group, while if everyone 35 or over used nuchal translucency screening and serum screening in a well-trained NT program before deciding about amnio, you could expect at best a 90% detection rate (80% with nuchal translucency screening alone)! You should however lower the amniocentesis rate in that population from 100% to 5%, and therefore lower the number of miscarriages from amniocentesis that occur to women who have normal babies. I suspect from my reading of this article that very few women under the age of 35 had NT screening done in any of the districts. The only way that NT screening will increase Down syndrome detection rates (rather than lowering them as seen above), will be to have it offered extensively to women under the age of 35. 2) Unknown rate of NT screening In the areas that offered NT screening, we have no idea of the proportion of patients who actually had it done. Certainly if only 5 or 10 or 20 percent of the women have it done, its impact in overall statistics of detection rates or invasive procedure rates is going to be very limited. To find out the value of NT screening, you need to compare the detection rate and invasive procedure rate in those that had NT screening compared to those who didn't; looking across the whole population it won't effect the overall numbers in a significant way unless a very high proportion of the women have NT screening done. 3) The years involved: This was a retrospective audit of Down syndrome cases that delivered (or terminated) between January 1, 1994 and December 31, 1999. Nuchal translucency screening was certainly in its infancy and development during most of the years of the study. 4) Training and certification status unknown: There is no mention of the training, skills, or expertise of those who were offering NT screening. We know that centers doing nuchal translucency screening where Fetal Medicine Foundation traiing and certification has not been done have far lower detection rates for Down syndrome than centers where FMF certification has been achieved. In the early years of the study there would have been no opportunity for them to have yet been properly trained and certified. The positives for NT testing: 1) One statistic that I was able to pull out of some of the tables in this paper would appear to show that nuchal translucency screening is pretty effective! In the 3 districts where nuchal translucency screening was considered to have been offered, there were 23 cases of Down syndrome detected because of nuchal thickening, and 5 false negative nuchal scans, for a detection rate of 82%. 2) Also, in the 3 districts that offered NT, of the 56 Down syndrome cases missed, there were only 4 false negative nuchal scans, which tells us that the other 52 patients didn't have the test done! It's hard to say that NT screening isn't effective if women weren't having having it done! You can read the original article at: http://bmj.com/cgi/reprint/325/7354/15.pdf Eric Deigan, M.D., FACOG, FRCSC Carolina Perinatal Associates, PLLC Cary, NC, USA ------------------------------ Date: Mon, 12 Aug 2002 19:39:21 -0500 ------------------------------ From: Terry J DuBose <tjdubose@juno.com> -- ------------------------------ To: ULTRASOUND@OBGYN.net Subject: Down Syndrome: New screening methods questioned Message-ID: <20020812.193923.1028.55.tjdubose@juno.com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary=--__JNP_000_6eff.1494.3e7d
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