[The prenatal detection of trisomy 13, 18, and 21: comparison of the advanced first trimester screening (AFS) with the first trimester screening according to Nicolaides].

PURPOSE

As a defined basic risk, the maternal background risk represents the most important influencing factor in the First Trimester Screening according to Nicolaides. However, the generated risk estimations often deviate from the observed clinical-practical values. The aims of this study were to perform a test performance analysis of the first trimester screening according to Nicolaides and its comparison with the novel "Advanced First Trimester Screening (AFS)" algorithm, which explicitly excludes the maternal background risk.

MATERIAL AND METHODS

At the Medical University of Hannover 2 743 pregnancies at 11 + 0 to 13 + 6 weeks of gestation underwent a combined ultrasonographic and biochemical First Trimester Screening. In a prospective approach, the risk calculation according to Nicolaides was performed with both the classic and the specific algorithm of the "ViewPoint-PIA Fetal database (PIA)" software. The risk calculation with the AFS algorithm was carried out in a retrospective approach.

RESULTS

The observed study population included seven cases of trisomy 21, two cases of trisomy 18, and one case of trisomy 13. Both the PIA and the AFS algorithm reached a sensitivity of 80 %, a false negative rate of 20 %, and a negative prediction value of 99.9 %. However, with a specificity of 97.01 %, a false positive rate of 2.99 %, and a positive prediction value of 11.76 % the AFS algorithm showed a better test performance than the PIA algorithm (96.06 %, 3.94 %, and 9.20 % respectively).

CONCLUSIONS

The calculation with AFS generated more precise risk estimations for trisomy 13, 18, and 21. An examination in large, prospective studies may be recommended to consider an introduction of this novel test strategy.