Cytogenetic abnormalities among spontaneously aborted previable fetuses.

We have reviewed spontaneously aborted fetuses of 9 to 20 developmental weeks. All fetuses with either external or internal developmental defects and those with maternal history of repeated spontaneous abortion were studied cytogenetically. Among 723 fetuses the cytogenetically proven prevalence of chromosome abnormalities was 5.8%. Inclusion of suspected chromosome abnormality based on morphologic findings resulted in an overall prevalence of only 7.1%. This prevalence and restricted spectrum of chromosome abnormalities, which included monosomy X, triploidy, gonosomal aneuploidy, trisomies 13, 18, and 21, resembled the prevalence and spectrum found among perinatal deaths and differed both in prevalence and type from those chromosome abnormalities found in spontaneous abortions occurring during the embryonic period. Monosomy X was the most common chromosome abnormality among previable fetuses. Both monosomy X and triploidy were more frequently detected in the early fetal period than in perinatal deaths. The combined prevalence of autosomal trisomies was equal to that which has been reported in the perinatal deaths. Chromosomal structural abnormalities, seen in perinatal deaths, were not found in our study.