THE PREDICTIVE VALUE OF CYTOGENETIC DIAGNOSIS AFTER CVS BASED ON 4860CASES WITH BOTH DIRECT AND CULTURE METHODS

Cytogenetic analysis was performed in 4860 chorionic villus samples by means of both direct preparation and long-term culture. The results o f the analysis were compared with a classification including all theor etical types of combinations between the chromosomal constitution of t he cytotrophoblast, extraembryonal mesoderm, and fetus, with the aim o f evaluating the cytogenetic variability along the trophoblast-embryo axis. Eighteen of 29 possible combinations were found demonstrating a considerable heterogeneity. A mosaic conceptus was found in 1.5 per ce nt of cases, with generalized mosaicisms and confined mosaicisms in 0. 2 and 1.3 per cent, respectively. Cytogenetic variability along the tr ophoblast-embryo axis was found in 1.42 per cent of cases. Results pos sibly leading to diagnostic errors (false-positive and false-negative results) were found in only 1.38 per cent. False-positive results of d irect preparation were the most commonly observed discrepancy (0.8 per cent), while the incidence of false-positive results of the culture m ethod and of both methods was 0.31 and 0.16 per cent respectively. The incidence of false-negative results was 0.1 per cent, with false-nega tive results of direct preparation 0.08 per cent and false-negative re sults of both methods 0.02 per cent. False-negative results of the cul ture method were not found. Our data confirm the high diagnostic accur acy of chorionic villus sampling and the utility of the combined use o f the two methods in minimizing diagnostic errors and in reducing the need for follow-up amniocentesis.