Contingent screening for Down syndrome—results from the FaSTER trial

Abstract

Abstract Objective Comparison of contingent, step‐wise and integrated screening policies. Methods Mid‐trimester Down syndrome risks were retrospectively calculated from FaSTER trial data. For contingent screening, initial risk was calculated from ultrasound measurement of nuchal translucency (NT), maternal serum pregnancy‐associated plasma protein (PAPP)‐A and free β‐human chorionic gonadotrophin (hCG) at 11–13 weeks, and classified positive (>1 in 30), borderline (1 in 30–1500) or negative. Borderline risks were recalculated using α‐fetoprotein, hCG, unconjugated estriol (uE 3 ) and inhibin at 15–18 weeks, and reclassified as positive (>1 in 270) or negative. For step‐wise screening, initial negative risks were also recalculated. For integrated screening, a single risk was calculated from NT, PAPP‐A and the second trimester markers. Results There were 86 Down syndrome and 32 269 unaffected pregancies. The detection rate for contingent screening was 91% and false‐positive rate was 4.5%; initial detection rate was 60%, initial false‐positive rate was 1.2% and borderline risk was 23%. Step‐wise screening had 92% detection rate and 5.1% false‐positive rate; integrated screening had 88% and 4.9% respectively. Conclusion As predicted by modelling, the contingent screening detection rate for a fixed false‐positive rate is comparable with step‐wise and integrated screening, but substantially reduces the number needing to return for second trimester testing. Copyright © 2008 John Wiley & Sons, Ltd.