Adverse obstetric outcomes are correlated with altered circulating hormone levels at the time implantation by the trophectoderm. What’ more, embryo freezing process may also have adverse effect on perinatal outcomes. This study aims to evaluate whether increasing interval time between a freeze-all cycle and a subsequent frozen-thawed single blastocyst transfer could have any effect on pregnancy and perinatal outcomes. This was a retrospective cohort study included the first single blastocyst transfer in artificially cycles of all patients who underwent a freeze-all cycle between January 1st, 2016 and September 30th, 2018. All patients were divided into two groups according to the time interval between oocyte retrieval and the day of first frozen-thawed embryo transferred (FET): Group 1 (immediate FET cycles) and Group 2 (delayed FET cycles). No significant differences were reported between the two groups regarding the rates of clinical pregnancy, live birth, biochemical pregnancy and pregnancy loss even after adjusting for measured confounding. When accounting for perinatal outcomes, gestational age, birth weight, delivery mode, fetus gender, preterm birth, gestational hypertension, GDM, placenta previa, fetal malformation and low birthweight also did not vary significantly between the two groups. Only the incidence of macrosomia was more frequently in the Group 2 compared with the Group 1 (AOR 3.886, 95%CI 1.153–13.103, P = 0.029) after adjusting with a multiple logistic regression model. We found delayed FET cycles for blastocyst transfer following freeze-all cycles may not improve the pregnancy outcomes. On the contrary, postponement of FET cycles may increase the risk of macrosomia. Therefore, FET cycles for blastocyst transfer should be done immediately to avoid adverse effects of delayed time on perinatal outcomes.

中文翻译：

---

全周期与随后的冻融单囊胚移植之间的时间间隔导致的妊娠妊娠和围产期结局

不良产科预后与滋养外胚层植入时循环激素水平的变化有关。此外，胚胎冷冻过程也可能对围产期结局产生不利影响。这项研究的目的是评估增加全冷冻周期和随后的冻融单胚泡移植之间的间隔时间是否可能对怀孕和围产期结局产生任何影响。这是一项回顾性队列研究，包括在2016年1月1日至2018年9月30日期间进行全冷冻周期的所有患者的人工循环中首次单次囊胚转移。根据卵母细胞之间的时间间隔将所有患者分为两组取回和首次冷冻融化胚胎移植（FET）的日期：第1组（立即FET周期）和第2组（延迟FET周期）。两组之间在临床妊娠率，活产率，生化妊娠率和妊娠流失率方面均未见明显差异，即使在调整了测量混杂因素之后也是如此。在考虑围产期结局时，两组之间的胎龄，出生体重，分娩方式，胎儿性别，早产，妊娠高血压，GDM，前置胎盘，胎儿畸形和低出生体重也没有显着差异。经过多因素Logistic回归模型调整后，与第1组相比，第2组中只有较大的发生率更高（AOR 3.886，95％CI 1.153-13.103，P = 0.029）。我们发现所有冷冻周期后囊胚转移的FET周期延迟可能不会改善妊娠结局。反之，FET周期的推迟可能会增加发生巨大儿的风险。因此，应立即进行胚泡转移的FET周期，以避免延迟时间对围产期结局的不利影响。