Embryo morphology and development are dependent on the chromosomal complement

Objective: To analyze embryo morphology in relation to the corresponding chromosomal status, in order to evaluate the effects of aneuploidy over fragmentation, delayed cleavage, and arrested cleavage. Design: Retrospective study. Setting: Reproductive Medicine Unit, Societa Italiana di Studi di Medicina della Riproduzione, Bologna, Italy. Patient(s): A total of 662 patients with a poor prognosis for pregnancy underwent 916 cycles of preimplantation genetic diagnosis for aneuploidy. Intervention(S): The chromosomes XY, 13, 15, 16, 18, 21, and 22 were analyzed in blastomeres biopsied from day 3 embryos. Main Outcome Measure(s): Embryo morphology, chromosomal status of the analyzed blastomeres, and spreading and reanalysis of nontransferred embryos. Result(s): The incidence of chromosomal abnormalities was significantly higher in arrested or slow-cleaving embryos, and in embryos cleaving too fast, compared to embryos with eight cells at 62 hours after insemination. The presence of an uneven number of blastomeres or fragments scattered in the perivitelline space was associated with an increased incidence of chromosomal abnormalities. Conclusion(s): A correlation between embryo development and chromosomal complement makes the incidence of chromosomal abnormalities significantly higher in embryos dividing according to a time frame and a symmetry plan which are different from what are expected. The type of fragmentation is also related to chromosomal status, which explains why the extrusion of fragments might severely affect embryo viability. (Fertil Steril (R) 2007;87: 534-41. (c) 2007 by American Society for Reproductive Medicine.)