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  • Title: First-trimester contingent screening for Down syndrome can reduce the number of nuchal translucency measurements required.
    Author: Vadiveloo T, Crossley JA, Aitken DA.
    Journal: Prenat Diagn; 2009 Jan; 29(1):79-82. PubMed ID: 19097036.
    Abstract:
    BACKGROUND: To assess the performance of a two-stage screening protocol for Down syndrome based on initial serum marker analysis for all women and nuchal translucency (NT) measurement only in women with intermediate risks. METHODS: Biochemical marker and NT data in 10 189 women who had had combined ultrasound and biochemical (CUB) screening, were re-analysed using the contingent model. A risk was calculated from the results of the pregnancy-associated plasma protein A (PAPP-A) and free beta human chorionic gonadotrophin (FbetahCG) measurements and maternal age. For risks between 1 in 42 and 1 in 1000, the likelihood ratio from the NT measurement was incorporated and assessed against a final cut-off risk of 1 in 250. RESULTS: A total of 3.1% unaffected and 61.4% Down syndrome pregnancies had risks>or=1:42. In women with risks<1 in 42 and >1 in 1000 (29%), a further 2.7% unaffected pregnancies and 27.3% Down syndrome pregnancies had risks above 1 in 250 when NT was incorporated. Overall detection rate was 88.6%, and false positive rate 5.8% (compared with 90.9% and 6.4% for CUB screening). NT measurements were required in 29% of women. CONCLUSIONS: Within first-trimester, contingent screening provides good sensitivity and specificity with the potential for considerable saving in ultrasound resources.
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