Age-independent first trimester screening for Down syndrome: analysis of three modified software programs with 6,508...

The conventional first trimester screening (FTS) method integrates maternal age into risk calculation. It was suggested that this concept increases the false-positive rate in older, and the false-negative rate in younger mothers.

Six thousand five hundred and eight combined FTS with known fetal outcome underwent regular risk calculation with the software programs Pia fetal database (PIA) (GE-ViewPoint, GE Medical Systems), prenatal risk calculation (PRC) (Version 1.0.61, gmt/nexus), and JOY (Version 2.1, PET software). The results were mathematically modified as if generated with age-independent software (PIA(mod), PRC(mod), and JOY(mod)).

17 of 40 trisomy 21 cases were present in women younger than 35. A right shift in the mean maternal age of false-negative cases occurred in all programs (PIA: 30.00, PIA(mod): 32.00, PRC: 30.00, PRC(mod): 32.25, JOY: 30.00, JOY(mod): 34.50). The overall false-positive rate declined by -40.03% (PIA(mod)), -38.64% (PRC(mod)), and -37.50% (JOY(mod)) and in women over 35 (40) years by -72.37, -73.45, and -73.20% (-89.04, -90.33, and -90.56%), being then as high as in the other age groups.

First trimester screening would become reasonable in women over 40 years. However, women over 35 would also be more often affected by false-negative results. The implications of a concept adaptation should be analyzed in a large prospective study.