Department of Obstetrics and Gynecology, University of Oulu, Oulu, Finland.
Hum Reprod. 2013 Sep;28(9):2425-31. doi: 10.1093/humrep/det251. Epub 2013 Jun 11.
Which clinical and laboratory factors affect live birth rate (LBR) after frozen-thawed embryo transfer (FET)?
Top quality embryo characteristics, endometrial preparation protocol, number of embryos transferred and BMI affected independently the LBR in FET.
FET is an important part of present-day IVF/ICSI treatment. There is limited understanding of the factors affecting success rates after FET.
STUDY DESIGN, SIZE, DURATION: This is a two-centre retrospective cohort study. Analysis was carried out on 1972 consecutive FET cycles in 1998-2007, with embryos frozen on Day 2. The primary outcome was LBR per cycle.
PARTICIPANTS/MATERIALS, SETTING, METHODS: We assessed the independent effect on LBR of the following variables: female age, female age at embryo freezing, BMI, diagnosis, primary versus secondary infertility, fertilization by IVF versus ICSI, pregnancy in the fresh cycle, type (spontaneous, spontaneous with luteal progesterone and estrogen/progesterone substitution) and rank of the FET cycle, as well as number and presence (yes versus no) of top quality embryo(s) at freezing, thawing and transfer, damaged thawed embryos and overnight culture.
In 78% of the cycles with top quality embryos frozen (n = 1319), at least one embryo still had high-quality morphology after thawing. Top quality embryo morphology observed at any stage of culture improved the outcome even if high-quality characteristics disappeared before transfer. LBRs after the transfer of a top quality embryo were similar in the FET (24.9%) and fresh cycles of the same period (21.9%). The chance of live birth increased significantly if ≥1 top quality embryo was present at freezing (odds ratio (OR) 1.85, 95% confidence interval (CI) 1.10-3.14), at thawing (OR 1.93, CI 1.20-3.11) or at transfer (OR 3.41, CI 2.12-5.48). Compared with spontaneous cycles with luteal support, purely spontaneous cycles (OR 0.58, CI 0.40-0.84) and hormonally substituted FET (OR 0.47, CI 0.32-0.69) diminished the odds of pregnancy. BMI (OR 0.96, CI 0.92-0.99) and transfer of two embryos versus one (OR 1.45, CI 1.08-1.94) were other factors that improved LBR after FET.
LIMITATIONS, REASONS FOR CAUTION: The sample sizes available in some subanalyses were small, limiting the power of the study.
The presence of ≥1 top quality embryo at any step of the freezing and thawing process increases the chance of pregnancy. The data do not support the freezing of all embryos for transfer in order to improve the outcome. A top quality embryo transferred in FET may even have the same potential as in a fresh cycle. On the contrary, LBR in the group with no top quality embryos frozen was quite low (10.4%), raising the question of whether a re-evaluation of freezing criteria is necessary to avoid costly treatments with a low success rate.
哪些临床和实验室因素会影响冷冻胚胎移植（FET）后的活产率（LBR）？
优质胚胎特征、子宫内膜准备方案、移植胚胎数量和 BMI 独立影响 FET 中的 LBR。
FET 是当今 IVF/ICSI 治疗的重要组成部分。对于影响 FET 后成功率的因素，我们的了解有限。
研究设计、大小和持续时间：这是一项两中心回顾性队列研究。分析了 1998-2007 年间进行的 1972 个连续 FET 周期，胚胎在第 2 天冷冻。主要结局是每个周期的 LBR。
参与者/材料、设置、方法：我们评估了以下变量对 LBR 的独立影响：女性年龄、胚胎冷冻时的女性年龄、BMI、诊断、原发性与继发性不孕、IVF 受精与 ICSI 受精、新鲜周期妊娠、FET 周期的类型（自发、自发加黄体支持、黄体支持加雌激素/孕激素替代）和等级，以及冷冻、解冻和移植时优质胚胎的数量和存在（有/无）、受损解冻胚胎和过夜培养。
在有优质胚胎冷冻的 78%（n=1319）的周期中，至少有一个胚胎在解冻后仍具有高质量的形态。即使在转移前优质特征消失，在任何培养阶段观察到的优质胚胎形态都能改善结果。FET 周期中转移优质胚胎的活产率与同期新鲜周期相似（FET：24.9%，新鲜周期：21.9%）。如果在冷冻时（优势比（OR）1.85，95%置信区间（CI）1.10-3.14）、解冻时（OR 1.93，CI 1.20-3.11）或转移时（OR 3.41，CI 2.12-5.48）存在≥1 个优质胚胎，活产的机会显著增加。与有黄体支持的自发周期相比，单纯自发周期（OR 0.58，CI 0.40-0.84）和激素替代 FET（OR 0.47，CI 0.32-0.69）降低了妊娠的可能性。BMI（OR 0.96，CI 0.92-0.99）和转移两个胚胎与一个胚胎（OR 1.45，CI 1.08-1.94）是改善 FET 后 LBR 的其他因素。
局限性、谨慎的原因：一些亚分析的可用样本量较小，限制了研究的效力。
在冷冻和解冻过程的任何步骤中存在≥1 个优质胚胎都会增加妊娠的机会。数据不支持为提高疗效而冷冻所有胚胎用于转移。FET 中转移的优质胚胎甚至可能与新鲜周期一样具有相同的潜力。相反，在没有冷冻优质胚胎的组中，LBR 相当低（10.4%），这引发了是否有必要重新评估冷冻标准以避免成功率低的昂贵治疗的问题。
