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Introduction: Blastocyst culture has been associated with higher implantation rates (IR) and pregnancy rates (PR). This could be explained by the synchrony between the endometrial and embryo development. However, prolonged culture to the blastocyst stage is associated with a high attrition rate of embryos. This could be because many of the embryos in the cleavage stage are actually abnormal embryos. Thus, these embryos could not survive sustained culture to blastocysts. This could also explain in part, the higher IR and PR associated with blastocyst culture. We wanted to evaluate the potential for blastocyst culture to reduce chromosomally abnormal embryos. Materials/Methods: This was a retrospective study performed in the TMC Fertility Centre (formerly known as Damansara Fertility Centre, Malaysia), involving 192 ART and PGD cases done between 1 January 2006 to 31 December 2007. All the embryos were biopsied and analysed using 5-probe fluorescence in-situ hybridization (FISH) for chromosomes 13, 18, 21, X and Y. All cleavage stage embryos with satisfactory quality (6 to 12 cells, less than 15% fragmentation) at 65 to 70 h post insemination were biopsied and a single cell was removed for chromosome analysis. Embryos that were not suitable for biopsy during the cleavage stage, either due to early compaction or suboptimal embryo quality, were cultured to the blastocyst stage. Biopsies of blastocysts were done at 132 to 137 h post insemination for blastocysts graded higher than BG3 BB. About three to eight trophectoderm cells were removed from each blastocyst. The aneuploidy rate for blastomeres derived from cleavage stage embryos was compared with the results obtained from trophectoderm cells collected from the blastocysts. Results: A total of 766 embryos were biopsied. Five hundred and ninety five embryos had a biopsy done at the cleavage stage. Of these, 294 (49.4%) were found to be normal while 301 embryos (50.5%) showed aneuploidy. In the blastocyst group, 171 blastocysts were biopsied. Of these, 106 blastocysts (62%) were normal and 65 (38%) showed aneuploidy. There was a significant reduction in aneuploidy rates in the blastocysts group (P < 0.005). The overall clinical pregnancy rate for all ART with PGD cases for 2006 was 51.0%, the delivery rate was 43.1% and the IR was 44.0% Conclusions: Prolonged culture of embryos to the blastocyst stage helps to improve the selection of chromosomally normal embryos for transfer. [ABSTRACT FROM AUTHOR]