[Prenatal risk index for fetal Down's syndrome with serum markers. Comment on the contribution by R. Benz, U. Müller, M. Krahner-Pilat, S. Wagner-Geuder, R. Terinde: Serum screening for Down's syndrome in women less than 35 years of age with an age-independent index].

5 years ago, maternal serum markers have been established for individual risk estimation of fetal Down syndrome. Recently Benz et al. presented an arbitrary age-independent risk index. Compared to the commonly applied statistical approach a 20% increase in detection rate was obtained by using the index (85% versus 65%). We recalculated data from 19,333 prospectively investigated pregnancies without trisomy 21 and 57 pregnancies with fetal Down syndrome using the proposed risk index. At the corresponding false-positive rate (7.9%) the age-independent detection rate was only 56%. This result indicates that the sensitivity cannot be increased by the Ulm index, when compared to statistical methods of risk estimation.