Chromosome studies of 500 couples with two or more abortions.

Chromosome studies of 500 couples with recurrent (two or more) spontaneous abortions revealed abnormal karyotypes in 50 partners (10%). There was no apparent relation with the number of abortions. The abnormalities were translocations (44%), mosaicisms (48%), and deletions or inversions (8%). In 20 cases the translocations were reciprocal and mainly maternal. Most mosaicisms involved the maternal X-chromosome. Studies of 78 relatives of the index patients identified another 24 carriers of a balanced translocation. Prenatal diagnosis was performed on 13 carriers of a balanced translocation and 16 carriers of a mosaicism because of their risk of an abnormal fetal karyotype causing serious congenital anomalies. These results illustrate the impact on the families. It is concluded that couples should have chromosome studies after two abortions and that maternal X-chromosomal mosaicism occurs as frequently as a balanced parental translocation.