Effects Of Vitrified Cryopreservation Duration And The Frozen State Of Embryos On The Outcomes Of Frozen Embryos

Objective:To explore the effects of vitrified cryopreservation duration and the frozen state of embryos on the recovery and pregnancy outcomes of frozen embryos.Methods:This retrospective study was conducted in reproductive medicine center of Ningxia Medical University General Hospital from June 2015 to June 2019.A total of 452 cycles of patients received frozen ET were selected,the general information and recovery and pregnancy outcomes following frozen ET were recorded.Vitrified cryopreservation duration was classified into four groups:group A??90 days?:186 cycles,group B?91-180 days?:118cycles,group C?181-360 days?:67 cycles,group D?>360 days?:81 cycles.The general information,recovery and pregnancy outcomes were compared among the four groups.Then,according to the development days and morphological scores of embryos?cleavage stage embryos were evaluated by Peter scoring method and blastocysts were evaluated by Gardner scoring method?when frozen,the embryos were divided into four groups:high-quality cleavage stage embryos group,non high-quality cleavage stage embryos group,high-quality blastocysts group and non high-quality blastocysts group,the recovery and pregnancy outcomes were compared among groups after stratification,then the effects of vitrified cryopreservation duration on the recovery and pregnancy outcomes of different frozen state of embryos were compared.Finally,Vitrified cryopreservation duration in group D was classified into three groups:group D1?361-1080 days?:36 cycles,group D2?1081-1800days?:32 cycles,group D3?>1800 days?:12 cycles,the recovery and pregnancy outcomes were compared among three groups.Result:1.Comparison of general information,recovery and pregnancy outcomes among the four groups with different cryopreservation durationA total of 956 embryos were thawed in 452 FET cycles.The cryopreservation duration of embryos were between 16-3091 days.The mean age of group A was younger than groups B and D?29.8±4.4 vs 31.0±4.7,31.7±4.7,P<0.05?,and the mean thickness of endometrium was thinner in group B than in groups A and D?10.5±1.7 vs 11.1±1.9,11.1±2.0,P<0.05?.There were no significant differences in the mean infertility years,levels of E₂ and P,and number of embryos transferred of patients among the four groups?P>0.05?.The rate of early pregnancy loss was lower in group C than in group A?17.9%vs 34.7%,P<0.05?;the rate of early pregnancy loss was lower in group C than in groups B and D,but the differences were not statistically significant.The rates of survival,intact,high quality embryos after thawing/before freezing,implantation,clinical pregnancy and early pregnancy loss had no significant differences among the four groups?P>0.05?.2.Comparison of recovery and pregnancy outcomes among groups of different frozen state of embryos?1?The intact rate was lower in high-quality cleavage stage embryos group than in non high-quality cleavage stage embryos group?65.8%vs 75.2%,P<0.05?,while the rates of implantation and clinical pregnancy were higher?30.6%vs 21.0%,49.0%vs 28.8%,P<0.05?;the rates of intact and implantation were much lower in high-quality cleavage stage embryos group than in high-quality blastocysts group?65.8%vs 87.5%,30.6%vs 57.1%,P<0.05?;the rates of survival,intact and implantation were much lower in high-quality cleavage stage embryos group than in non high-quality blastocysts group?84.9%vs 94.0%,65.8%vs 94.0%,30.6%vs 42.2%,P<0.05?.?2?The implantation rate was much lower in non high-quality cleavage stage embryos group than in high-quality blastocysts group?21.0%vs 57.1%,P<0.05?;the rates of intact,implantation and clinical pregnancy were much lower in non high-quality cleavage stage embryos group than in non high-quality blastocysts group?75.2%vs 94.0%,21.0%vs 42.2%,28.8%vs 56.1%,P<0.05?.?3?The rates of survival,intact,high-quality embryos after thawing/before freezing,implantation,clinical pregnancy and early pregnancy loss between high-quality blastocysts group and non high-quality blastocysts group had no significant differences?P>0.05?.3.Comparison of the effects of vitrified cryopreservation duration on the recovery and pregnancy outcomes of different frozen state of embryosIn the high-quality cleavage stage embryos group,the implantation rate was higher in group A than in group D?35.2%vs 24.8%,P<0.05?,the remaining indicators were no statistical differences among the four groups?P>0.05?.In the non-high quality cleavage stage embryos group and non high-quality blastocysts group,all indicators were no statistical differences among the four groups?P>0.05?.4.Vitrified cryopreservation duration in group D was classified into three groups,the recovery and pregnancy outcomes were compared among three groupsThe rates of survival and intact were much lower in group D3 than in groups D1 and D2?66.6%vs 93.1%,66.6%vs 87.3%?44.4%vs 84.7%,44.4%vs 78.9%,P<0.05?,the remaining indicators were no statistical differences among the three groups?P>0.05?.Conclusion:1.Vitrified cryopreservation duration had no significant effects on the recovery and pregnancy outcomes of frozen embryos,but after further stratified,it was found that cryopreservation duration exceeding 1800 days might affect the recovery outcome of frozen embryos.2.In the vitrified frozen transfer cycles,whether high quality or not,blastocysts stage embryos had better recovery and pregnancy outcomes than cleavage stage embryos.3.Vitrified cryopreservation duration had no significant effects on the recovery and pregnancy outcomes of the different frozen state of embryos.