Preimplantation aneuploid embryos undergo self-correction in correlation with their developmental potential

Objective: To investigate the incidence of embryos' self-correction during preimplantation development in terms of mosaicism and in correlation with its developmental stage. Design: Prospective study to compare the chromosome status of embryos on day 3 with that of day 5, in correlation with their developmental stage. Setting: In vitro fertilization unit of a university-affiliated hospital. Patient(s): Eighty-three aneuploid embryos. Intervention(s): Fluorescence in situ hybridization (FISH) reanalysis. Main Outcome Measure(s): Day 3 embryos classified as mosaic or chromosomally abnormal by preimplantation genetic screening (PGS) were reanalyzed on day 5. The results were evaluated in correlation with the embryos' developmental stage. Result(s): Out of 83 day 3 aneuploid embryos, 15 (18.1%) were diagnosed with mosaicism. The FISH reanalysis on day 5 demonstrated that 27 embryos (32.6%) were partly or entirely normal disomic. Of these 83 aneuploid embryos, 8 (9.7%) underwent complete self-correction. The PGS results demonstrated that 26.5% of the embryos were trisomic, of which 41.0% underwent trisomic rescue by day 5. Self-correction was in correlation with the embryo's developmental stage, i.e., 38.1% of aneuploid embryos that developed to the blastocyst stage underwent self-correction compared with only 12.5% of embryos that only cleaved after biopsy. Conclusion(s): Our results demonstrate that self-correction of aneuploid and mosaic embryos occurs probably more significantly during development toward the blastocyst, stage than in delayed embryos. In addition, trisomic embryos correct themselves more than other aneuploidies. These findings suggest that PGS results must be interpreted with caution. (Fertil Steril (R) 2009;92:890-6. (C)2009 by American Society for Reproductive Medicine.)