Development of medians generators for the calculation of MoM for the first-trimester Down syndrome maternal serum markers

The Down syndrome risk calculation software, Fast Screen pre I plus, from Thermo Fisher Scientific, converts the First-trimester maternal serum markers concentrations (PAPP-A and hCG beta) into degrees of extreme (DoE). To meet the requirements of the French legislation as well as those of the certified biologists for Down syndrome screening, a conversion tool for DoE into multiple of the median (MoM), intermediate reference value for the screening, was developed. In absence of any median polynomial allowing to obtain MoM easily, the calculations were made first on the basis of the polynomials centiles from the software. The subsequent reviews of the risk algorithms showed the fragility of this approach based on the Gaussian hypothesis. Medians generators, calculated from the data of the Kryptor club's biologists, were established.