A high degree of aneuploidy in frozen-thawed human preimplantation embryos

We have studied the chromosomal content in 68 normally fertilised freeze-th awed human embryos of good morphology from 34 patients with an avenge mater nal age of 32,6 years. Forty embryos showed post-thaw cellular division and twenty-eight post-thaw cleavage arrest. After spreading of the embryos on microscope slides, analysis of chromosomes X, Y, 15, 16, 17 and 18 was perf ormed using two rounds of fluorescent in situ hybridisation (FISH). Accordi ng to the results, the embryos were divided into four groups: (I) normal, a ll nuclei uniformly diploid, (II) diploid mosaics, normal diploid blastomer es in combination with abnormal blastomeres, (III) abnormal, all nuclei abn ormal, (IV) chaotic, the chromosome constitution varies randomly from cell to cell. Approximately 25% of the embryos had normal number of the chromoso mes tested, while the majority of the embryos were abnormal. Most of the ab normal embryos were diploid mosaics (57%). This was true for the embryos sh owing; cleavage division as well as the embryos showing cleavage arrest,Our data show a slightly higher incidence of abnormal embryos compared to thos e obtained with FISH in non-cryopreserved embryos and confirm that the majo rity of preimplantation embryos fertilised in vitro contain abnormal blasto meres. The results, mechanisms, significance and implications are discussed .