Abnormal karyotypes in semi-direct chorionic villus preparations of women with different cytogenetic risks.

Among 3499 cytogenetically investigated semi-direct chorionic villus samples, 219 (6.3 per cent) abnormal karyotypes were encountered. The karyotypes were considered certainly abnormal (generalized abnormal with high probability) in 109 cases (3.1 per cent), and in 110 cases (3.1 per cent) uncertainly abnormal (potentially confined to the placenta), requiring further investigation. Of these 110 uncertain abnormalities, the cytogenetic result turned out to be finally abnormal representing generalized abnormality in 36 cases (32.7 per cent), finally normal representing confined placental mosaicism (CPM) in 69 cases (62.7 per cent), and remained undetermined in 5 instances (4.5 per cent). The rate of the numbers of certainly abnormal and all (certainly + uncertainly) abnormal results, the certainty rate, and that of generalized abnormalities and all abnormalities (generalized abnormalities + CPM cases), the predictive value, are strongly correlated with the cytogenetic risk. Therefore, we advise chorionic villus sampling for cytogenetic investigation only in women with a cytogenetic risk equal to or exceeding that of a 40-year-old pregnant woman. Because of the high rate of prenatal follow-up investigations after the finding of uncertain results in semi-direct villi, semi-direct and cultured villi should be karyotyped simultaneously.