Nuchal Translucency-Based Down Syndrome Screening: Barriers to Implementation
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
References (10)
- et al.
First and second trimester evaluation of risk (FASTER) trialprincipal results of the NICHD Down Syndrome Screening Study
Am J Obstet Gynecol
(2003) - et al.
First-trimester sonographic screening for Down syndrome
Obstet Gynecol
(2003) - et al.
UK multicenter project on assessment of risk of trisomy 21 by maternal age and fetal nuchal-translucency thickness at 10–14 weeks of gestation
Lancet
(1998) - et al.
Antenatal Down syndrome screening in the United States in 2001a survey of maternal-fetal medicine specialists
Am J Obstet Gynecol
(2002) - et al.
First and second trimester antenatal screening for Down’s syndromethe results of the Serum, Urine and Ultrasound Screening Study (SURUSS)
Health Technol Assess
(2003)
Cited by (15)
Quality assessment of routine nuchal translucency measurements: A North American laboratory perspective
2008, Genetics in MedicineEducation and quality review for nuchal translucency ultrasound
2005, Seminars in PerinatologyUnited States' experience in nuchal translucency measurement: variation according to provider characteristics in over five million ultrasound examinations
2021, Ultrasound in Obstetrics and GynecologyNoninvasive approaches to prenatal diagnosis: Historical perspective and future directions
2019, Methods in Molecular BiologyNoninvasive prenatal testing for trisomy 21: Challenges for implementation in Australia
2013, Australian and New Zealand Journal of Obstetrics and GynaecologyFormative assessment based on an audit and feedback improves nuchal translucency ultrasound image quality
2013, Journal of Ultrasound in Medicine