ABSTRACT
Objective To explore the impact factors for post-thaw embryo survival rate and clinical pregnancy rate in frozen-thawed embryo transfer program. Methods The clinical data of 573 cycles of frozen-thawed embryo transfers were retrospectively analysed. Groups were divided according to the pre-freeze embryo quality, pre-freeze embryonic developmental stage, frozen-thawed embryo quality and cryopreservation technique, respectively, and post-thaw embryo survival rates and/or clinical pregnancy rates were compared among groups. Results The clinical pregnancy rate of high quality pre-freeze embryo was significantly higher than that of low quality pre-freeze embryo (31.8% vs 20.0%) (P< 0.05). There was no significant difference in the post-thaw survival rates and clinical pregnancy rates between embryos frozen at day 2 of ferrtilization and those frozen at day 3 of ferrtilization(79. 1% vs 82.9% and 25.5% vs 31.2%, respectively) (P>0.05). The clinical pregnancy rates of the transfer cycles only with fully intact embryos and with mixed embryos were significantly higher than that only with partially damaged embryos(36.7% vs 24.1% and 29.2% vs 24.1%, respectively)(P<0.05). The post-thaw survival rate and post-thaw high-quality embryo rate were significantly higher in those processed with modified cryopreservation technique than in those processed with original cryopreservation technique (82.0% vs 66.3% and 50.0% vs 27.5%, respectively)(P<0.05). Conclusion Pre-freeze embryo quality, post-thaw embryo survival rate and post-thaw embryo quality have a positive correlation to subsequent clinical pregnancy rate. Favorable cryopreservation technique may ensure the success of post-thaw embryo recovery and transfer.