Effect Of Blastocyst Formation Time On Clinical Outcomes In Single Frozen-thawed Good-quality Blastocyst Transfer Cycles

Objective: To analyze the clinical data of good-quality single blastocysts transplanted at different development speeds during frozen-thawed cycles,compare pregnancy outcomes and birth outcome,and provide guidance for blastocyst selection strategies during frozenthawed cycles.Methods: This study analyzed retrospectively the concerned clinical data of infertile patients who were undergoing first good-quality single frozen-thawed blastocyst transfer in the Reproductive Medicine center of the Shengjing Hospital of China Medical University from January 2015 to November 2018.According to the inclusion and exclusion criteria,it totally included 1032 cycles,and according to the day of blastocyst expansion,1032 cycles were divided into the 5th day blastocyst group(D5 group,n = 668)and the 6th day blastocyst group(D6 group,n = 364).In order to compare the pregnancy outcomes between the two groups,we adopted the HCG positive rate,implantation rate,clinical pregnancy rate,total live birth rate multiple pregnancy rate,ectopic pregnancy rate,abortion rate,early abortion rate and so on.Further to compare the birth outcome,465 cases of singleton term birth following transfer were selected.,according to the day of blastocyst expansion,it is divided into the 5th day blastocyst group(A group,n =313)and the 6th day blastocyst group(B group,n = 152).The main outcomes measured were absolute birth weight,Z-score adjusted for gestational age and gender,and incidence of low birth weight rate,incidence of macrosomia,deformity rates,sex-ratio and so on.Results: 1.The HCG positive rate,clinical pregnancy rate,live birth rate,single birth rate of D5 group were higher than that of D6 group,but the difference was not statistically significant(P> 0.05).2.There was no significant difference in ectopic pregnancy rate,multiple pregnancy rate,abortion rate,early abortion rate,preterm birth rate,and cesarean section rate between the group D5 and the group D6(P> 0.05).3.There was no significant difference in the weight,incidence of low body weight,incidence of macrosomia,incidence of very small age for gestational age,incidence of small age for gestational age,incidence of large age for gestational age,incidence of very large age for gestational age,deformity rates and proportion of male infants in the group D5 and the group D6.Conclusion: 1.The HCG positive rate,clinical pregnancy rate,live birth rate,single birth rate of D5 good-quality blastocysts were higher than that of D6 good-quality blastocysts,however,the difference was not statistically significant.2.There is no significant difference in birth outcome of good-quality blastocysts of different expansion formation speed.3.There is no significant difference in development potential of goodquality blastocysts of different expansion formation speed.