STUDY QUESTION Is there an association between serum LH levels prior to progesterone administration and live birth rate (LBR) in artificial frozen-thawed embryo transfer (FET) cycles? SUMMARY ANSWER : Low serum LH levels on the day before progesterone initiation in artificial frozen-thawed blastocyst transfer cycles of ovulatory women are associated with a lower LBR. WHAT IS KNOWN ALREADY In artificial FET cycles, exogenous oestrogen and progesterone are administered sequentially to mimic the serum hormone pattern similar to the natural cycle. In oestrogen-only phase, the supplemental oestrogen causes thickening of the endometrium and is sometimes accompanied by a rise in serum LH. However, whether the endogenous LH level in artificial FET cycles is related to clinical outcomes remains unclear. STUDY DESIGN, SIZE, DURATION A retrospective cohort study including 3469 artificial frozen-thawed blastocyst transfer cycles was conducted at a tertiary-care academic medical centre between February 2014 and January 2020. PARTICIPANTS/MATERIALS, SETTING, METHODS A total of 3469 frozen blastocyst transfer cycles were stratified into four groups based on the quartiles of serum LH level before progesterone initiation: <25th percentile (LH < 8.79 mIU/ml), 25–50th percentile (8.79 ≤ LH ≤ 13.91 mIU/ml), 51–75th percentile (13.91 < LH ≤ 20.75 mIU/ml) and >75th percentile (LH > 20.75 mIU/ml). The serum LH level >75th percentile group was considered as the reference group. Patients with polycystic ovarian syndrome or other ovulatory disorders were excluded from the study. We also excluded cycles with an endometrial thickness <7 mm before progesterone initiation and patients with intrauterine adhesions and uterine abnormalities. In order to avoid the interference of BMI, all patients were divided into two categories based on the overweight threshold: BMI <25 kg/m2 and ≥25 kg/m2, and the impacts of serum LH levels on LBR were investigated separately. Univariable and multivariable logistic regression analysis were performed to adjust for potential confounders. EmpowerStats software and R-project were used to build smooth curve fitting models. MAIN RESULTS AND THE ROLE OF CHANCE Compared with the reference group, the implantation rate significantly decreased with low LH levels (<25th percentile) on the day before progesterone initiation (odds ratio [OR] = 0.74; 95% CI, 0.64–0.86; P = 0.001). Accounting for major covariates, low LH levels were associated with a relatively lower LBR (adjusted OR = 0.649; 95% CI, 0.531–0.794; P < 0.001), mainly due to a lower implantation rate, lower clinical pregnancy rate and higher pregnancy loss rate. Moreover, in the patients with BMI <25 kg/m2, low LH was associated with a lower LBR (P < 0.001); while in the overweight subgroup, LBR and LH were not correlated (P = 0.823). LIMITATIONS, REASONS FOR CAUTION The main limitation of this study is its retrospective design. Owing to the relatively small number in the overweight group, the results of the overweight subgroup should be interpreted with caution. WIDER IMPLICATIONS OF THE FINDINGS The evidence provided in this study shows the importance of serum LH levels on the day before progesterone initiation in patients undergoing artificial FET cycles. Hypothalamic dysfunction may be one of the important causes of a relatively low LH, which is related to impaired pregnancy outcomes. Serum LH levels may be used as one of the clinical indicators to predict pregnancy outcomes. STUDY FUNDING/COMPETING INTEREST(S) No funding and no competing interest were involved in this study. TRIAL REGISTRATION NUMBER NA.

中文翻译：

---

排卵期女性人工冻融囊胚移植周期中孕酮给药前内源性 LH 水平与活产率的关系

研究问题 孕酮给药前的血清 LH 水平与人工冻融胚胎移植 (FET) 周期中的活产率 (LBR) 之间是否存在关联？总结答案：在排卵期妇女的人工冻融囊胚移植周期中，孕酮开始前一天的低血清 LH 水平与较低的 LBR 相关。已知情况 在人工 FET 周期中，外源性雌激素和黄体酮依次给药以模拟类似于自然周期的血清激素模式。在仅雌激素阶段，补充雌激素会导致子宫内膜增厚，有时还会伴有血清 LH 升高。然而，人工 FET 周期中的内源性 LH 水平是否与临床结果相关仍不清楚。研究设计，尺寸，持续时间 2014 年 2 月至 2020 年 1 月，在一家三级医疗学术医疗中心进行了一项包括 3469 个人工冻融囊胚移植周期的回顾性队列研究。参与者/材料、设置、方法总共 3469 个冷冻囊胚移植周期被分为四个基于孕酮开始前血清 LH 水平四分位数的组：<25% (LH < 8.79 mIU/ml)、25-50% (8.79 ≤ LH ≤ 13.91 mIU/ml)、51-75% (13.91 < LH ≤ 20.75 mIU/ml) 和 > 75% (LH > 20.75 mIU/ml)。血清LH水平＞75%的组被认为是参考组。患有多囊卵巢综合征或其他排卵障碍的患者被排除在研究之外。我们还排除了子宫内膜厚度 < 的周期。孕激素开始前 7 毫米和宫腔粘连和子宫异常的患者。为避免BMI的干扰，将所有患者根据超重阈值分为BMI＜25 kg/m2和≥25 kg/m2两类，分别考察血清LH水平对LBR的影响。进行单变量和多变量逻辑回归分析以调整潜在的混杂因素。EmpowerStats 软件和 R-project 用于构建平滑曲线拟合模型。主要结果和机会的作用与参考组相比，在孕酮开始前一天，植入率显着降低，LH 水平低（<25%）（优势比 [OR] = 0.74；95% CI，0.64-0.86 ;P = 0.001)。考虑主要协变量，低 LH 水平与相对较低的 LBR 相关（调整后的 OR = 0.649；95% CI，0.531-0.794；P < 0.001），主要是由于较低的着床率、较低的临床妊娠率和较高的流产率。此外，在 BMI <25 kg/m2 的患者中，低 LH 与低 LBR 相关（P < 0.001）；而在超重亚组中，LBR 和 LH 不相关（P = 0.823）。限制，谨慎的原因 本研究的主要限制是其回顾性设计。由于超重组的人数相对较少，因此应谨慎解释超重亚组的结果。研究结果的更广泛意义 本研究提供的证据表明，在接受人工 FET 周期的患者中，孕酮开始前一天血清 LH 水平的重要性。下丘脑功能障碍可能是 LH 相对较低的重要原因之一，这与妊娠结局受损有关。血清 LH 水平可作为预测妊娠结局的临床指标之一。研究资金/竞争利益 本研究不涉及资金和竞争利益。试用注册号 NA。