First-trimester screening for Down syndrome in France combining fetal nuchal translucency measurement and biochemical markers

Background In France, there is a strictly regulated National Screening Programme for Down syndrome, based on second-trimester maternal serum markers, A prospective study of nuchal translucency together with retrospective evaluation of maternal serum markers was carried out to inform decisions on whether to move the programme to the first trimester. Methods Between January 1998 and June 2001, all women who presented for their prenatal care at 12 participating maternity units were, regardless of age, invited to provide a blood sample and to attend for an NT scan at 11 to 13 weeks. The results were used to derive Gaussian distribution parameters. Detection and false-positive rates were computed in two ways: statistical modelling and directly. The cut-off risk was 1 in 250 at term. Results A total of 5694 women with singleton pregnancies were screened including 26 with Down syndrome and 24 with other aneuploidies. The model-predicted detection and false-positive rates for combined ultrasound and serum screening were 8 1 and 4.5% compared to 64 and 6.0% for ultrasound alone. The directly observed rates were 73 and 4.7%. compared to 62 and 5.0% respectively. Conclusion In France, first-trimester screening with nuchal translucency and maternal serum markers is likely to achieve a high screening efficiency. This has important implications for the national screening policy. Copyright (C) 2003 John Wiley Sons, Ltd.