The impact of cryopreservation timing and embryo factors on clinical outcome of frozen-thawed embryo transfer cycles

Objective To investigate the impact of cryopreservation timing and embryo quality on the clinical outcome of frozen-thawed embryo transfer cycles(FET).Methods A retrospective analysis was performed on 417 FET cycles.The patients were divided into different groups according to freezing time,embryo blastomere count and good-quality embryo count.Frozen-thawed effects and clinical outcomes in different cryopreservation timings and embryo qualities were observed.Results The good-quality embryo rate of D2 embryo was significantly higher than that of D3 embryo(56.84% vs 48.82%),though with significantly lower clinical pregnancy rate(27.61% vs 38.52%).However,there was no significant difference in the post-thaw embryo survival rate or abortion rate between D2 embryo and D3 embryo(83.50% vs 79.44%,and 10.81% vs 10.09%,P 0.05).In D2 embryo group,the post-thaw embryo survival rate and total blastomere survival rate were significantly higher in cells exceeded 4-cell than those less than 4-cell(89.35% vs 79.11%,and 42.01% vs 30.22%,respectively,P 0.05).In D3 embryo group,they were significantly higher in cells exceeded 6-cell comparing with those less than 6-cell(86.52% vs 72.43%,and 41.13% vs 31.07%,respectively,P 0.01).When more and more were transferred,The clinical pregnancy rate and multiple pregnancy rate were significantly positively correlated with the good-quality embryo count(P 0.05).Conclusion The D3 embryo cryopreservation in FET provides better clinical outcome.The embryos quality and good-quality embryo count transferred is close correlated with FET outcomes,suggesting the key factors to FET cycles.