Elsevier

Seminars in Perinatology

Volume 29, Issue 4, August 2005, Pages 272-276
Seminars in Perinatology

Nuchal Translucency-Based Down Syndrome Screening: Barriers to Implementation

https://doi.org/10.1053/j.semperi.2005.05.002Get rights and content

Nuchal translucency sonography represents an important step forward in screening for Down syndrome. It is likely that a range of screening programs that rely on nuchal translucency sonography will become popular for general population screening. However, a number of practical implementation issues remain to be resolved before widespread utilization of this technique can be endorsed. This paper addresses some of these issues, including sonographer training, standardized nuchal translucency sonography protocol, ongoing nuchal translucency quality assurance programs, how to interpret Down syndrome risk, availability of first trimester diagnosis, and how to combine screening tests across different gestational ages.

Section snippets

Initial Sonographer and Sonologist Training

A meta-analysis of studies of nuchal translucency-based screening for Down syndrome suggests an overall Down syndrome detection rate of 77%, at a 6% false positive rate.2 However, when the 34 studies in this analysis are evaluated separately, Down syndrome detection rates vary from a low of 29% (4% false positive rate), to a high of 100% (5% false positive rate).2 The most likely reason for the large variation in screening results relates to significant variation in sonographer training and

Standardized Nuchal Translucency Sonographic Technique

The elements of an accepted nuchal translucency sonographic technique are summarized in Table 1.2 These elements draw on the experience derived from the Fetal Medicine Foundation and the FASTER Research Consortium.

Some practitioners prefer to restrict nuchal translucency sonography to a minimum gestational age of 11 weeks, because the potential benefit of first trimester general fetal anatomy survey might be optimized in the late first trimester. However, the FASTER Trial has demonstrated that

Ongoing Nuchal Translucency Quality Assurance

Considerable variability in nuchal translucency quality occurs in large-scale population-based research studies.1, 4 For example, in the recently completed FASTER Trial in which nuchal translucency measurements were attempted for over 38,000 patients at 15 centers throughout the United States, sonographers failed to obtain technically satisfactory imaging in 7% of cases.1 In almost 3% of cases, the initial sonographer felt that their imaging was adequate, but later central image review

Interpreting Down Syndrome Risks

How to define a normal or abnormal nuchal translucency measurement can be challenging. Use of a single millimeter cutoff (such as 2.5 or 3.0 mm) is inappropriate because nuchal translucency measurements normally increase with gestational age (by approximately 15% to 20% per gestational week from 10 to 13 weeks). Instead, gestational-specific cutoffs are required, which might include 95th percentile values, MoM values (multiples of the median nuchal translucency measurement for that gestational

Availability of First Trimester Diagnosis

Provision of Down syndrome risk assessment in the first trimester will require the widespread availability of first trimester diagnostic techniques. Since amniocentesis before 15 weeks’ gestation has been associated with increased risks of pregnancy loss and fetal clubfoot, the only acceptable invasive test to provide definitive fetal karyotype information in the first trimester is chorionic villus sampling (CVS).6, 7 However, CVS is not widely available throughout the United States, with

Combining Screening Tests at Different Gestational Ages

With the increasing range of Down syndrome screening tests now available to practitioners in both the first and second trimesters of pregnancy, confusion will likely develop when patients have more than one screening test performed. It is not valid to perform separate Down syndrome risk assessments at different gestational ages by providing independent estimations of risk on each test. For example, if a particular population has been subjected to first trimester screening, approximately 80% of

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