Improving the clinical outcomes by extended culture of day 3 embryos with low blastomere number to blastocyst stage following frozen-thawed embryo transfer.

PURPOSE This study aimed to investigate whether the extended culture of day 3 (D3) embryos with low blastomere number to blastocyst following frozen-thawed embryo transfer improved the clinical outcomes. METHODS This was a retrospective study of clinical data of women undergoing in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles in the Tangdu Hospital. The patients were divided into groups with 4-5, 6, 7-9 and > 9 cells based on the blastomere number of D3 embryos. The clinical outcomes were compared. RESULTS In fresh transfer cycles, the implantation and clinical pregnancy rates significantly decreased, while the abortion rate significantly increased in the groups with 4-5 and 6 cells compared with those with 7-9 and > 9 cells. In frozen-thawed transfer cycles, the clinical pregnancy and implantation rates for a single blastocyst transfer cycle showed no significant differences in the groups with 4-5 and 6 cells compared with those with 7-9 and > 9 cells. However, the abortion rate was significantly higher in the group with 4-5 cells than in that with 7-9 and > 9 cells. In the double blastocyst transfer cycle, the clinical pregnancy rate showed no significant differences among the groups with 4-5, 6, and 7-9 cells. CONCLUSION The implantation and clinical pregnancy rates of D3 embryos with 6 cells significantly decreased; these embryos were not considered as high-quality embryos. Extended culture of D3 embryos with ≤ 6 blastomeres to blastocysts, particularly 6-cell embryos, resulted in a similar clinical pregnancy rate as that of blastocysts derived from D3 embryos with ≥ 7 blastomeres.