Chromosome abnormalities in early pregnancy analyzed by direct chromosome preparation of chorionic villi.

Chorionic villi chromosome analysis was performed on 1,186 cases of induced abortion between the 5th and 11th week of gestation. The total incidence of major chromosome abnormalities, including numerical and structural chromosomal changes as well as mosaics and polyploids, was 4.5% (53 cases). The most common abnormalities were trisomy 21 (5 cases), trisomy 16 (4 cases), and monosomy X (4 cases). The incidence of chromosome abnormalities increased with the advancing age of the mother.