Frequencies of fetal chromosomal abnormalities at prenatal diagnosis: 10 years experiences in a single institution

We present frequencies of fetal chromosomal abnormalities in 4,907 prenatal cytogenetic examinations at Samsung Cheil Hospital from 1988 to 1997 for 1 0 yr duration. Prenatal karyotypes were undertaken in 3,913 amniotic fluid samples, 800 chorionic villi samples, and 194 percutaneous umbilical blood samples. The frequency of fetal abnormal karyotypes was 3.1% (150 cases). N umerical chromosome abnormalities were 87 cases (1.8%) and structural aberr ations of chromosomes were 63 cases (1.3%), In the numerical chromosomal ab normalities, the frequency of trisomy 21 was by far the highest (36 cases), followed by trisomy 18 in 22 cases and sex chromosome aneuploidies in 19 c ases. In the structural chromosomal aberrations, 5 cases had the inversions in chromosome 2, 7, 17, and Y, Chromosomal deletions in 6 cases and additi ons in 4 cases were analysed. Of the remaining 47 translocation in abnormal fetuses, reciprocal translocation was in 26 cases and Robertsonian translo cation in 21 cases. Among them, 41 cases were balanced translocation and 6 were unbalanced. Thirty five cases of translocation were inherited from one of the parents. Four had de novo chromosome rearrangements, and 8 cases we re unknown.