Ekelund, Charlotte Kvist3; Wright, Dave4; Ball, Susan4; Kirkegaard, Ida10; Nørgaard, Pernille6; Sørensen, Steen7; Jørgensen, Finn Stener6; Friis-Hansen, Lennart8; Uldbjerg, Niels10; Tørring, Niels11; Petersen, Olav Bjørn10; Tabor, Ann3
1 Obstetrics and Gynaecology, Faculty of Health Sciences, Aarhus University, Aarhus University2 Department of clinical biochemistry, Faculty of Health Sciences, Aarhus University, Aarhus University3 Klinik for føtalmedicin og ultralydskanning 4002, Rigshospitalet4 Fetal Medicine Foundation, London5 Department of Clinical Medicine - Department of Obstetrics and Gynaecology, Department of Clinical Medicine, Health, Aarhus University6 Gynækologisk-Obstetrisk afd, Hvidovre Hospital7 Klinisk-Biokemisk afd, Hvidovre Hospital8 Klinisk-Biokemisk afd, Rigshospitalet9 Department of Clinical Medicine - Department of clinical biochemistry, Department of Clinical Medicine, Health, Aarhus University10 Department of Clinical Medicine - Department of Obstetrics and Gynaecology, Department of Clinical Medicine, Health, Aarhus University11 Department of Clinical Medicine - Department of clinical biochemistry, Department of Clinical Medicine, Health, Aarhus University
Objective: To prospectively evaluate the screening performance of first trimester combined screening for trisomy 21 using a double set of biochemical markers Methods: Three fetal medicine departments in Denmark participated in the study. Screening for trisomy 21 was set up as a two-step approach with an early blood sample taken prior to the NT scan, and another blood sample taken at the time of the NT scan. PAPP-A and free β-hCG were measured on both the early and the late samples, and Multiples of the Median (MoM) values were calculated in addition to the corresponding trisomy 21 risk. Using statistical modelling we estimated detection rates (DR) and false positive rates (FPR) when using early sampling, late sampling or combinations of early and late sampling. Results: We collected two blood samples in 25 pregnancies affected by trisomy 21 and in 3942 control pregnancies. The early samples were taken between gestational week 8+0 to 13+6, and the late samples were taken between week 11+3 and 14+6. The median interval between the samples was 17 days (range 1-40 days). The best performance of the combined screening was obtained using PAPP-A from the early sample and free β-hCG from the late sample, with a 95% DR for a 2.5 % FPR at a cut off 1:100. Conclusion: Using repeated biochemical sampling in the first trimester with early PAPP-A and late free β-hCG can optimize the screening performance of combined screening for trisomy 21.