News methods for second trimester screening of Down syndrome: statistical analysis of the use of nasal bone length and prenasal thickness

Abstract

Introduction: Sonographic measurements of nasal bone length and prenasal soft tissue thickness are ultrasonographic methods for prenatal screening of Down syndrome. Aim: The aim of the authors was to create a local normogram for nasal bone length and prenasal soft tissue thickness measurements and to test the performance of different statistical methods. Method: Euploid (N = 1500) and trisomy 21 foetuses (N = 10) studied between April 2008 and December 2013 were included. Nasal bone length and prenasal thickness measurements were performed at the Medisono Fetal and Maternal Health Research Centre, Szeged, and cytogenetic tests were performed at the Department of Medical Genetics, University of Szeged, Hungary. Normograms were created with different number of patients (N = 100, 300, 500, 750. 1000 and 1500) and using 3 different statistical methods (linear regression, square-based regression, and box-plot analysis). Results: The results indicated that at least 1000 measurements are strongly recommended for the normograms. The increase of patient number improved the efficacy of the normograms in each of the 3 statistical methods used for analysis. In general practice box-plots provides a better performance over the other screening methods. However, advanced level screening requires local linear normograms for the best screening results. Conclusion: The use of box-plots is recommended for the use in the daily practice but regression-based normograms are necessary for advanced prenatal screening. Orv. Hetil., 2014, 155(47), 1876–1881.