Examination of a first-trimester Down syndrome screening concept on a mix of 11,107 high- and low-risk patients at a private center for prenatal medicine in Germany.

OBJECTIVE: To assess the performance of a combined first-trimester screening concept for trisomies 21, 18 and 13 applied to a low- and high-risk patient sample in a specialized private center for prenatal medicine. STUDY
DESIGN: The quality of different first-trimester screening algorithms (risk calculation based on maternal age and nuchal translucency alone, maternal age and serum parameters (free beta-hCG and PAPP-A) alone and a combination of both) was evaluated in a study population of low- and high-risk cases for fetal aneuploidies. All measurements were performed between the 11th+0 and 13th+6 weeks of gestation during the study period from November 2000 to December 2006, in accordance with the guidelines of the Fetal Medicine Foundation (FMF), London.
RESULTS: Of 11,107 women included in the study, we had a complete follow-up on 10,668. The difference between the detection rate was insignificant for both the low-risk and the high-risk groups. In the overall study population, 52 of 59 cases of trisomy 21 were detected when a pre-defined cut-off of 1:300 was applied (detection rate (DR) 88.1%; 95% confidence interval (CI): 79.8-96.4 and false-positive rate (FPR) 4.9%; 95% CI: 4.5-5.3). For trisomies 13 and 18 with a pre-defined cut-off of 1:150, 26 of 32 cases were detected (DR 81.3%; 95% CI: 67.8-94.8 and FPR 0.7%; 95% CI: 0.5-0.9). The highest sensitivity was between 11+0 and 11+6 weeks of gestation with all cases of trisomy 21 detected with a FPR 5.1%; 95% CI: 3.7-6.5.
CONCLUSION: In our study population of different risk categories, the detection rate using the combined risk calculation based on maternal age, fetal NT, maternal PAPP-A and free beta-hCG levels was superior to the application of either parameter alone.