Author(s): Wright D, Bradbury I, Benn P, Cuckle H, Ritchie K
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Abstract OBJECTIVE: To present a first and second trimester Down syndrome screening strategy, whereby second-trimester marker determination is contingent on the first-trimester results. Unlike non-disclosure sequential screening ('the Integrated test'), which requires all women to have markers in both trimesters, this allows a large proportion of the women to complete screening in the first trimester. METHODS: Two first-trimester risk cut-offs defined three types of results: positive and referred for early diagnosis; negative with screening complete; and intermediate, needing second-trimester markers. Multivariate Gaussian modelling with Monte Carlo simulation was used to estimate the false-positive rate for a fixed 85\% detection rate. The false-positive rate was evaluated for various early detection rates and early test completion rates. Model parameters were taken from the SURUSS trial. RESULTS: Completion of screening in the first trimester for 75\% of women resulted in a 30\% early detection rate and a 55\% second trimester detected rate (net 85\%) with a false-positive rate only 0.1\% above that achievable by the Integrated test. The screen-positive rate was 0.1\% in the first trimester and 4.7\% for those continuing to be tested in the second trimester. If the early detection rate were to be increased to 45\% or the early completion rate were to be increased to 80\%, there would be a further 0.1\% increase in the false-positive rate. CONCLUSION: Contingent screening can achieve results comparable with the Integrated test but with earlier completion of screening for most women. Both strategies need to be evaluated in large-scale prospective studies particularly in relation to psychological impact and practicability. Copyright (c) 2004 John Wiley & Sons, Ltd.
This article was published in Prenat Diagn
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