Effects of duration of in vitro culture on clinical pregnancy outcomes after vitrification frozen blastocyst resuscitation
Objective:To investigate the effects of duration of in vitro culture on clinical pregnancy outcomes after thawing and resuscitation of vitrified dilated blastocyst.Methods:A retrospective analysis was conducted on 1 867 cycles of Day 5(D5)and Day 6(D6)blastocyst transfer with vitrification freezing in Reproductive Medicine Center of Northwest Women's &Children's Hospital between January 1,2021 and December 31,2022.Based on the duration of in vitro culture,women were divided into Group A(＜2 hours,n=958)and Group B(2 to 4 hours,n=909).Furthermore,based on the number of transferred blastocysts,two subgroups were formed as group A1(1 blastocyst transferred,n=843),group B1(1 blastocyst transferred,n=798)and group A2(2 blastocysts transferred,n=115),group B2(2 blastocysts transferred,n=111).Differences among the groups were compared in terms of HCG positive rate,clinical pregnancy rate,implantation rate,multiple pregnancy rate,early miscarriage rate,and final live birth rate.Results:There were no significant differences in mean age,infertile years,endometrial thickness and basic hormone levels between groups A1 and B1 as well as A2 and B2(P＞0.05).In terms of pregnancy outcomes,there were no significant differences in HCG positive rate,clinical pregnancy rate,embryo implantation rate,multiple birth rate,early miscarriage rate,ectopic pregnancy rate and live birth rate between group A1 and group B1(P＞0.05),but HCG positive rate in group A2 was significantly higher than that in group B2(91.30％vs.79.28％,P＜0.05).The clinical pregnancy rate(81.74％vs.71.17％),implantation rate(61.30％vs.54.05％)and live birth rate(67.83％vs.63.06％)in group A2 were slightly higher than those in group B2(P＞0.05).The Logistic analysis showed that＜2 hours of the duration of in vitro culture was an independent factor influencing HCG positive rate[OR=2.210,95％CI(1.028,4.752),P=0.042]in the cycles of 2 blastocysts transfer.Conclusions:Double blastocysts should be transferred within 2 hours after thawing to achieve better clinical outcomes,while there were no significant differences in clinical outcomes when single blastocyst was transferred within 4 hours after thawing.
Thawed blastocyst transferDuration of in vitro cultureClinical outcome
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