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To the Editor: Dr Smith-Bindman and colleagues 1 have summarized a large amount of potentially useful data but, I believe, have misinterpreted or ignored data that support the use of ultrasonographic markers of Down syndrome. The results of their meta-analysis show that most ultrasonographic markers as isolated findings are statistically associated with an increased risk for fetal Down syndrome (2.8- to 17-fold greater). Furthermore, the combination of anomalies and markers were identified in 69% of fetuses with trisomy 21 (Table 3). This is consistent with other centers reporting detection rates of 59% to 82% 4 when markers are combined with structural anomalies (observed in less than 20% of affected fetuses before 20 weeks at most centers).2 - 3 Even using outdated assumptions, the authors found a benefit for all markers except choroid plexus cyst among high-risk patients (defined as a relatively low risk of 1 in 300).
In addition, the authors assume a prevalence of 1:700 for trisomy 21. A more recent estimate is 1:504. 5 Using this prevalence with the authors' 69% sensitivity and 8% false-positive rate for ultrasound screening, detecting 1 affected case would require screening 730 women with a loss of 0.47 normal fetuses.
The reduction of risk of detecting fetal Down syndrome applies to a normal ultrasound finding, not to an absence of any individual marker. Indeed, a negative likelihood ratio (LR) for an individual marker has little clinical relevance. Using their data (Table 3), a normal ultrasound finding has a negative LR of 0.34 (31/92). This value agrees with negative LRs reported by others in the range of 0.3 to 0.46 and corresponds to a 60% to 70% reduction of risk following a normal ultrasound result.
Smith-Bindman et al also suggest that a single marker in a low-risk patient would be considered a positive screen result. Like biochemical markers, ultrasonographic markers cannot be viewed in isolation but must be interpreted together with other clinical variables, such as advanced maternal age.2 For example, an isolated echogenic intracardiac focus (LR, 2.8) in a 25-year-old woman (baseline risk, 1:1040) would result in a postultrasound risk of 1:372. This result should be considered a positive finding but a negative ultrasound screen result, and it should not alter obstetric management.
Like biochemical analytes, ultrasonographic markers can provide important information about the risk of fetal Down syndrome when used appropriately but can cause confusion and needless anxiety when the results are misinterpreted.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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