ABSTRACT
Objective To compare the influence of cryopreservation duration on quality of rozen-thawed embryo and clinical outcome in frozen-thawed transfer cycles. Methods A retrospective study was performed to evaluate the clinical outcomes and quality of rozen-thawed embryo of frozen embryo transfer(FET)cycles includ-ing freezing cycles and vitrification cycles. FET cycles were divided into 4 group acorrding to the storage duration of vitrified embryos:1~6 months group ,7~12 months group ,13~24 months group and ≥ 25 months group. Result There was no significant difference in recovery rate ,clinical pregnancy rate and abortion rate (98.1%, 99.0%,96.8%&95.7%;54.4%,55.4%,49.6%&51.5%;0.7%,8.9%,9.4%&11.1%;P>0.05). The embryos recovery rate and clinical pregnant rate after vitrification were significantly higher than programmed freezing (P<0.05). The blastocyst recovery rate in group A was significantly higher than the cleavage stage embryo recov ery rate in group B(P<0.05). Conclusions Vitrification has better effects on cryopreservation and clinical outcomes. Blastocyst may be the best stage for vitrifying and freezing of embryo.