['To evaluate whether the developmental potential of the blastocyst is affected by the number of trophectoderm (TE) cells biopsied in preimplantation genetic diagnosis (PGD) cycles.', 'Retrospective study.', 'University-affiliated center.', 'Women underwent PGD cycles of blastocyst biopsy and fluorescence in situ hybridization analysis.', 'Not applicable.', 'Biopsied TE\xa0cell number of blastocysts, survival, and implantation rates.', 'The biopsied TE\xa0cell number was affected by the TE quality and experience of different embryologists. The diagnostic efficiency increased when from one to five cells were biopsied (86.7%, 91.7%%, 96.0%, 96.8%, to 98.7%) and was maximized when more than six cells were biopsied. To compare the clinical efficiencies, blastocysts were divided into four groups according to biopsied TE\xa0cell number: 1-5, 6-10, 11-15, and 16-41. For the blastocysts with grade A\xa0TE score, no significant difference was observed in the survival and implantation rates among the four groups. For the blastocysts with grades B and C\xa0TE scores, the survival rates showed no significant differences among the four groups, but a significant decreasing trend in implantation rates was observed with increasing biopsied TE\xa0cell number.'] Is number of biopsied trophectoderm cells likely to affect the implantation potential of blastocysts with poor trophectoderm quality?