Confined placental mosaicism in spontaneous abortions

One hundred and eleven early spontaneous abortions were examined for the presence of confined chromosomal mosaicism. For each specimen amnion, chorionic plate, chorionic villi, and umbilical cord were sampled and processed using long term tissue culture techniques. In addition, direct preparation techniques were applied to the chorionic villi. Thus both the cytotrophoblast and the villous stroma fibroblasts of the chorionic villi were assessed. These placental tissues were representative of three developmental cell lineages: (1) trophoblast via cytotrophoblast, (2) extraembryonic mesoderm via chorionic villous stroma and chorionic plate, and (3) embryonic ectoderm via amnion and umbilical cord. Fifteen metaphases per tissue were cytogenetically analyzed. Forty spontaneous abortions yielded cytogenetic results, and consisted of 11 karyotypically normal and 29 abnormal specimens. The chromosomal anomalies observed were trisomy, triploidy, structural anomalies, monosomy X, and confined mosaicism involving trisomic and tetraploid cell lines. Ten percent of the studied specimens revealed a confined mosaic constitution suggesting that this chromosomal defect is common in the spontaneous abortion population. Segregation or cleavage errors are thought to have taken place within 3 diploid and 1 trisomic conceptus. The timing of the mitotic error can be estimated from the affected placental tissues. Although the contribution of confined chromosomal mosaicism to the etiology of pregnancy loss is not clearly understood, any alteration of the genomic content of developmental cell lineages may effect the function of the resulting tissue(s) and therefore the survival or demise of the conceptus.Medicine, Faculty ofMedical Genetics, Department ofGraduat