STUDY QUESTION Is there a significant intra-individual variability of serum progesterone levels on the day of single blastocyst Hormone Replacement Therapy-Frozen Embryo Transfer (HRT-FET) between two consecutive cycles? SUMMARY ANSWER No significant intra-individual variability of serum progesterone (P) levels was noted between two consecutive HRT-FET cycles. WHAT IS KNOWN ALREADY In HRT-FET cycles, a minimum P level on the day of embryo transfer is necessary to optimise reproductive outcomes. In a previous study by our team, a threshold of 9.8 ng/ml serum P was identified as significantly associated with the live birth rates in single autologous blastocyst transfers under HRT using micronized vaginal progesterone (MVP). Such patients may benefit from an intensive luteal phase support (LPS) using other routes of P administration in addition to MVP. A crucial question in the way towards individualising LPS is whether serum P measurements are reproducible for a given patient in consecutive HRT-FET cycles, using the same LPS. STUDY DESIGN, SIZE, DURATION We conducted an observational cohort study at the university-based reproductive medicine centre of our institution focusing on women who underwent at least two consecutive single autologous blastocyst HRT-FET cycles between January 2019 and March 2020. PARTICIPANTS/MATERIALS, SETTING, METHODS Patients undergoing two consecutive single autologous blastocyst HRT-FET cycles using exogenous oestradiol and vaginal micronized progesterone for endometrial preparation were included. Serum progesterone levels were measured on the morning of the Frozen Embryo Transfer (FET), by a single laboratory. The two measurements of progesterone levels performed on the day of the first (FET1) and the second FET (FET2) were compared to evaluate the intra-individual variability of serum P levels. Paired statistical analyses were performed, as appropriate. MAIN RESULTS AND THE ROLE OF CHANCE Two hundred and sixty-four patients undergoing two consecutive single autologous blastocyst HRT-FET were included. The mean age of the included women was 35.0 ± 4.2 years. No significant intra-individual variability was observed between FET1 and FET2 (mean progesterone level after FET1: 13.4 ± 5.1 ng/ml vs after FET2: 13.9 ± 5.0; P = 0.08). The characteristics of the embryo transfers were similar between the first and the second FET. Forty-nine patients (18.6%) had discordant progesterone levels (defined as one progesterone measurement > and one ≤ to the threshold of 9.8 ng/ml) between FET1 and FET2. There were 37/264 women (14.0%) who had high intra-individual variability (defined as a difference in serum progesterone values >75th percentile (6.0 ng/ml)) between FET1 and FET2. No specific clinical parameter was associated with a high intra-individual variability nor a discordant P measurement. LIMITATIONS, REASONS FOR CAUTION This study is limited by its retrospective design. Moreover, only women undergoing autologous blastocyst HRT-FET with MVP were included, thereby limiting the extrapolation of the study findings to other routes of P administration and other kinds of endometrial preparation for FET. WIDER IMPLICATIONS OF THE FINDINGS No significant intra-individual variability was noted. The serum progesterone level appeared to be reproducible in >80% of cases. These findings suggest that the serum progesterone level measured on the day of the first transfer can be used to individualize luteal phase support in subsequent cycles. STUDY FUNDING/COMPETING INTEREST(S) No funding or competing interests TRIAL REGISTRATION NUMBER N/A.

中文翻译：

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激素替代治疗周期中冷冻囊胚移植当天血清孕酮水平的个体差异

研究问题 在两个连续周期之间的单囊胚激素替代疗法 - 冷冻胚胎移植 (HRT-FET) 当天，血清孕酮水平是否存在显着的个体内差异？摘要答案 在两个连续的 HRT-FET 周期之间，未发现血清孕酮 (P) 水平存在显着的个体差异。已知信息 在 HRT-FET 周期中，胚胎移植当天的最低 P 水平对于优化生殖结果是必要的。在我们团队之前的一项研究中，9.8 ng/ml 血清 P 的阈值被确定与使用微粉化阴道黄体酮 (MVP) 进行 HRT 的单次自体囊胚移植的活产率显着相关。此类患者可能受益于强化黄体期支持 (LPS)，除 MVP 外还使用其他磷给药途径。 LPS 个体化的一个关键问题是，使用相同的 LPS，在连续的 HRT-FET 周期中，特定患者的血清 P 测量是否可重复。研究设计、规模、持续时间我们在我们机构的大学生殖医学中心进行了一项观察性队列研究，重点关注在 2019 年 1 月至 2020 年 3 月期间接受至少两次连续单自体囊胚 HRT-FET 周期的女性。参与者/材料，背景、方法 接受两个连续单自体囊胚 HRT-FET 周期的患者，使用外源性雌二醇和阴道微粉化黄体酮进行子宫内膜准备。冷冻胚胎移植 (FET) 当天早上，由一个实验室测量血清黄体酮水平。对第一个 (FET1) 和第二个 FET (FET2) 当天进行的两次黄体酮水平测量进行比较，以评估血清 P 水平的个体内变异性。酌情进行配对统计分析。主要结果和机会的作用 纳入了 264 名连续接受两次单自体囊胚 HRT-FET 治疗的患者。纳入女性的平均年龄为 35.0 ± 4.2 岁。 FET1 和 FET2 之间未观察到显着的个体内差异（FET1 后平均孕酮水平：13.4 ± 5.1 ng/ml vs FET2 后：13.9 ± 5.0；P = 0.08）。第一次 FET 和第二次 FET 的胚胎移植特征相似。 49 名患者（18.6%）在 FET1 和 FET2 之间具有不一致的孕酮水平（定义为一项孕酮测量值≥和一项≤阈值 9.8 ng/ml）。 FET1和FET2之间有37/264名女性(14.0％)具有高个体内变异性(定义为血清孕酮值的差异＞75%(6.0ng/ml))。没有特定的临床参数与高个体内变异性或不一致的 P 测量相关。局限性和注意事项本研究因其回顾性设计而受到限制。而且，仅纳入接受自体囊胚 HRT-FET 和 MVP 的女性，从而限制了研究结果对其他 P 给药途径和其他类型的 FET 子宫内膜准备的外推。研究结果的更广泛意义 没有发现显着的个体差异。血清孕酮水平在＞80％的病例中似乎是可重复的。这些发现表明，第一次移植当天测量的血清孕酮水平可用于在后续周期中个体化黄体期支持。研究资助/竞争利益 无资助或竞争利益 试验注册号 不适用。