冻融胚胎移植周期中第5天4BC囊胚与第6天4BB囊胚移植的妊娠结局比较OA

Objectives:To compare the clinical pregnancy outcomes and perinatal outcomes between single 4BC blastocyst transfer on day 5 and 4BB blastocyst transfer on day 6 in frozen-thawed embryo transfer(FET)cycles. Methods:The clinical data of 312 single frozen-thawed blastocyst transfer cycles at Xingtai Meihe Reproductive & Genetic Hospital between January 1,2018 and December 31,2024 were retrospectively analyzed.The cycles were divided into two groups according to blastocyst developmental stage and grade:Group A(4BC blastocyst transferred on day 5,n=106)and Group B(4BB blastocyst transferred on day 6,n=206).Baseline characteristics,clinical pregnancy outcomes and perinatal outcomes were compared between the two groups.Subgroup analyses of pregnancy outcomes were further conducted stratified by maternal age(＜35 years and ≥35 years). Results:There were no significant differences in baseline data between Group A and B(P＞0.05).Group A showed a tendency of higher clinical pregnancy rate(60.38％vs.49.51％)and live birth rate(46.23％vs.37.38％)compared with Group B,but without statistical significance(P＞0.05).No significant differences were observed in ectopic pregnancy rate,miscarriage rate and preterm birth rate between the two groups(P＞0.05).Age-stratified subgroup analysis demonstrated that in patients aged＜35 years,Group A had slightly higher clinical pregnancy rate(58.82％vs.47.90％)and live birth rate(41.18％vs.37.72％)than Group B,but with no statistical difference(P＞0.05).In contrast,in patients aged ≥35 years,the live birth rate of Group A(66.67％vs.35.90％)was significantly higher than that of Group B(P＜0.05). Conclusions:In frozen-thawed blastocyst transfer cycles,for women younger than 35 years,there was no significant difference in clinical pregnancy rate and live birth rate between the two transfer strategies,while for those aged 35 years and above,single 4BC blastocyst transfer on day 5 can be preferred.