Screening for fetal Down's syndrome with maternal serum markers--an experience in Italy.

The effectiveness of maternal serum alpha-fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin in screening for Down's syndrome (DS) was evaluated on 840 women who underwent amniocentesis for fetal karyotype on account of their age. The risk of a DS pregnancy was established using the method of Wald et al. (1988b), which combines the age-specific risk with that indicated by the levels of the three serum markers. In women over 35, at cut-off risk levels of 1:250 and 1:380, the false-positive rate was 24 and 34 per cent, respectively. In all nine cases of DS, the estimated risk was higher than 1:250. The best screening strategy with the lowest false-positive rate was obtained by combining the three serum markers. The results suggest that this kind of screening can be proposed during genetic counselling for women under 35 and older women wishing to avoid the risk of miscarriage induced by amniocentesis.