Blastocyst culture and cryopreservation to optimize clinical outcomes of warming cycles

Surplus embryos available for cryopreservation in fresh cycles are considered as having good potential for future use. However, the optimal stage of embryo cryopreservation remains unclear. In this study, 1190 patients with surplus embryos on day 3 were divided into two groups: cleavage-stage embryo cryopreservation (control group) and blastocyst cryopreservation (blastocyst group). The clinical outcomes of the subsequent warming cycles were evaluated. The proportion of cycles with blastocyst formation was 73.8% in the blastocyst group. Although in the blastocyst group, the cancellation rate of blastocyst transfer was increased due to lack of blastocysts available for cryopreservation, the blastocyst group achieved significantly higher rates of clinical pregnancy/cycle (43.2% versus 34.9%; P = 0.003), pregnancy/transfer (59.5% versus 35.4%; P < 0.001) and implantation (46.5% versus 22.2%; P < 0.001) from the first warming cycle compared with the control group. In an embryo-number classified analysis, the clinical pregnancy rate was also higher in the blastocyst group. However, the cumulative pregnancy was similar between the two groups. Blastocyst culture as an embryo selection tool will not improve embryo viability but it will help patients to achieve pregnancy more quickly. Extended culture of surplus embryos to the blastocyst stage for cryopreservation optimizes the clinical outcomes.Surplus embryos available for cryopreservation in fresh cycles have been considered as having good potential for future use. However, it remains unclear whether cleavage-stage embryo cryopreservation on day 3 or further extended culture with blastocyst cryopreservation on day 5 or 6 is of most benefit to patients. This prospective study was undertaken to evaluate the clinical outcomes of vitrified–warmed embryo transfer cycles according to cryopreservation of embryos at different stages. The study enrolled 1190 patients with surplus embryos on day 3, who were divided into two groups: cleavage-stage embryo cryopreservation (control group) and blastocyst cryopreservation (blastocyst group). The proportion of cycles with blastocyst formation in the blastocyst group was 73.8%. Although the cancellation rate of blastocyst transfer in the blastocyst group was increased due to lack of blastocysts available for cryopreservation, the blastocyst group achieved significantly higher rates of clinical pregnancy/cycle (43.2% versus 34.9%; P = 0.003), clinical pregnancy/transfer (59.5% versus 35.4%; P < 0.001) and implantation (46.5% versus 22.2%; P < 0.001) from the first warming cycle as compared with the control group. In an embryo-number classified analysis, the clinical pregnancy rate was also higher in the blastocyst group. However, the cumulative pregnancy was similar between the two groups. In conclusion, blastocyst culture as an embryo selection tool will not improve embryo viability but it will help patients to achieve pregnancy more quickly. Extended culture of surplus embryos to the blastocyst stage for cryopreservation optimizes the clinical outcomes of the subsequent warming cycles.