目的 分析比较培养至第6天（D6）或第7天（D7）的囊胚及第5天（D5）囊胚在解冻移植周期中的助孕结局，探讨延长囊胚培养时间是否会增加不良的产科和新生儿结局。方法 单中心回顾性队列研究，纳入2010年1月至2023年12月期间在北京大学第三医院生殖中心接受单个冻融囊胚移植2325周期。其中D7囊胚移植周期465周期、D6囊胚移植周期930周期及D5囊胚移植周期930周期，3组按1∶2∶2比例进行匹配，匹配因素包括夫妻双方年龄、女性体质指数、不孕原因及受精方式。比较D6和D7组与D5组在基础特征、妊娠结局、产科并发症及新生儿结局方面的差异。结果 D7组原发性不孕比例高于D5组（65.8% vs. 57.5%，P<0.05）。D6组（63.5%）及D7组（38.5%）优质形态胚胎比例均显著低于D5组（77.30%，P<0.001）。与D5组相比，D7组的生化妊娠率（32.5% vs. 47.2%）、临床妊娠率（26.0% vs. 42.2%）及活产率（17.6% vs. 32.2%）均明显降低（P<0.001）。然而，在多胎妊娠率（D6：1.1%，D5：1.8%，D7：2.5%）及流产率（D6：22.5%，D5：20.9%，D7：28.9%）方面，差异无统计学意义。D6组妊娠并发症发生率低于D5组（6.0% vs. 11.2%，P=0.011），而D7组与D5组无明显差异（13.2% vs. 11.2%，P>0.05）。中孕期及晚孕期胎儿畸形终止妊娠共3例：D6组发现1例唐氏综合征和1例胎儿发育畸形，D7组发现1例双侧肾发育不全。早产率（D6： 8.8%，D5：10.7%，D7：12.2%）、先天性缺陷发生率（D6：1.1%，D5：1.0%，D7：2.4%）、平均出生体重[D6：3400 g（3060~3700 g），D5：3435 g（3100~3750 g）；D7：3400 g（3100~3690 g）]和平均分娩孕周[D6：39孕周（38~39孕周），D5：39孕周（38~39孕周），D7：39孕周（38~39孕周）]之间差异均无统计学意义。结论 在囊胚复苏周期中，与第5天囊胚移植相比，第6天或第7天囊胚移植在妊娠期并发症、新生儿结局方面无差异。

Objective To compare the pregnancy and neonatal outcomes of blastocysts cultured to Day 6（D6）or Day 7（D7）with those cultured to Day 5（D5）in frozen-thawed embryo transfer（FET）cycles，and to investigate whether extended blastocyst culture increases the risk of adverse obstetric and neonatal outcomes.Methods This single-center retrospective cohort study included 2，325 patients who underwent single frozen-thawed blastocyst transfer at the Reproductive Center of Peking University Third Hospital between January 2010 and December 2023.Among them，465 cycles were D7，930 cycles were D6，and 930 cycles were D5.The three groups were matched at a 1∶2∶2 ratio based on maternal and paternal age，female body mass index（BMI）cause of infertility，and fertilization method.Clinical characteristics，pregnancy outcomes，obstetric complications，and neonatal outcomes were compared between the D6/D7 groups and the D5 group.Results The proportion of primary infertility was significantly higher in D7 group compared to D5 group（65.8% vs. 57.5%，P<0.05）.D6 and D7 groups showed significantly lower proportions of top morphological grade embryos（63.5% vs. 77.3%，P<0.001；38.5% vs. 77.3%，P<0.001）.D7 group had significantly lower biochemical pregnancy rates（32.5% vs. 47.2%，P<0.001），clinical pregnancy rates（26.0% vs. 42.2%，P<0.001），and live birth rates（17.6% vs. 32.2%，P<0.001）compared to D5 group.However，no significant differences were found in multiple pregnancy rates（D6：1.1%，D5：1.8%，D7：2.5%），and miscarriage rates（D6：22.5%，D5：20.9%，D7：28.9%）between D5 and D6/D7 groups.While D6 group had a significant difference in pregnancy complications（D6：6% vs. D5：11.2%，P=0.011），no significant differences were observed between D5 and D7 groups（D5：11.2% vs. D7：13.2%）.The terminations of mid-trimester and late pregnancy with fetal malformation included three cases，a Down syndrome and a fetal developmental malformation in D6 group，and a bilateral renal agenesis in D7 group.Compared to D5 group，D6 or D7 group was not different in preterm birth rates（D6：8.8%，D5：10.7%，D7：12.2%），congenital birth defects rates（D6：1.1%，D5：1.0%，D7：2.4%），average birth weight[D6：3400（3060-3700），D5：3435（3100-3750），D7：3400（3100-3690）]，and average gestational age at birth[D6：39（38-39），D5： 39（38-39），D7：39（38-39）].Conclusion In frozen-thawed embryo transfer cycles，transferring Day 6 or Day 7 blastocysts does not significantly increase the risk of pregnancy-related complications or adverse neonatal outcomes compared to Day 5 blastocysts.