Introduction Combined nuchal translucency (cNT) screening was established within a 3000 delivery unit at a cost of £18000. The uptake, changes in sensitivity and specificity and effect on the rate of invasive prenatal testing were analysed.
Methods NHS NT screening was introduced November 2009 over 3 months. A retrospective dataset was assembled from our central screening service, the regional cytogenetics laboratory and local databases over 3 financial years from April 2008 to March 2011.
Results All comparison reflect 2008/2009 compared to 2010/2011. Global uptake of Downs screening increased from 62% to 72.9%. In 2008/2009 25% of Downs screening was carried out using private cNT compared to 2010/11 with 94% requesting NHS cNT. Screen positive (high risk) rates decreased from 2.9% to 1.8% with the number of invasive diagnostic procedures decreasing from 44 to 21. The proportion of these using chorionic villus biopsy increased from 2.6% to 41% (includes investigation of cystic hygroma).
In 2008/9 1 Downs syndrome pregnancy was detected compared to 4 in 2010/11. All were detected following cNT. None following quadruple testing. In 2008/2009 1 Downs syndrome pregnancy occurred following a low risk result (quadruple testing) compared to 3 in 2010/2011 (2 cNT and 1 quadruple testing).
Conclusion cNT is a cost efficient means of Downs syndrome screening that has reduced the rate of invasive testing. There appears to have a been a marginal improvement in detection rates but larger numbers are required for statistical analysis.
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