First-trimester Down syndrome screening performance in the Dutch population; how to achieve further improvement?

Objective To study the performance of the first‐trimester combined test between 2004 and 2006 compared to a previous period to investigate changes in time and identify reasons for sub‐optimal performance. Methods Serum samples were analysed for pregnancy‐associated plasma protein A (PAPP‐A) and the free β subunit of human chorionic gonadotrophin (fβ‐hCG). Nuchal translucency (NT) was measured between 10 and 14 weeks. Tests were considered screen positive, if their calculated Down syndrome (DS) risk was at least 1 in 250 at term. Results A total of 20 293 singleton pregnancies were included in the analysis. The median maternal age fell from 35.7 to 34.3 years. The overall median weight‐corrected multiple of the median (MoM) values of PAPP‐A and fβ‐hCG were 1.12 and 1.03, respectively. The median MoM value of NT was 0.89 and increased from 0.82 to 0.96. Sixty‐six DS cases were detected by the screening test. The detection rate (DR) for DS was 75.9%, with a FPR of 3.3%. Conclusion The performance of the first‐trimester test has improved over the years. A better performance of the NT measurement was the main reason, although NT assessment should further be improved. In addition, a better setting of the medians for the biochemical parameters may contribute to a higher DR. Copyright © 2009 John Wiley & Sons, Ltd.