Análisis de resultados «falsos negativos» para trisomía 21 en los programas de cribado combinado de primer trimestre: una herramienta para la mejora de la calidad

Abstract

IntroductionAnalysis of false negatives (FN) detected in Prenatal Screening Programme for trisomy 21 (T21) by First Trimester Combined Screening (CC1°T) could be a tool to help improve the final results and the overall quality of these programmes. The objective is to evaluate the characteristics of the FN cases for T21 and compare them with the true positives (TP). Material and methodsA retrospective study (January 2005 - December 2012). FN and TP results for CC1°T were selected, excluding multiple gestations. The analyzed variables were maternal age and weight, gestational age (at the time of biochemical testing), nuchal translucency (NT) measurement in millimeters and in Multiples of Medians (MoM), serum concentrations and corrected MoM of free β-HCG and PAPP-A and biochemical risk. Statistical analysis was carried out with SPSS® 22 software. ResultsMedian maternal age, median NT (in millimeters and in MoM) and median biochemical risk were lower in FN cases, however, maternal weight was higher, all these differences were statistically significant. We did not find significant differences in the rest of variables. ConclusionsThe occurrence of FN is caused by multiple factors. We found significant differences in maternal weight and NT, as well as borderline significance in differences of MoM of PAPP-A, therefore, it is essential to use the correct weight at the time of biochemical testing and, most important, ensure the quality of NT and PAPP-A measurement. Maternal age determines the previous risk and final result; so it is significant that our FN cases appeared in younger pregnant.