Ovarian stimulation for IVF is known to affect luteal phase function. The endometrium in IVF cycles is thus subject to an altered endocrinological environment and to a possible direct effect of the ovarian stimulation therapy. Factors influencing the endometrial receptivity in such cycles are poorly understood. Studies comparing the endometrium in IVF cycles with natural cycles as controls have shown premature secretory changes in the post-ovulatory and early luteal phase of IVF cycles, followed by a large proportion of dyssynchronous glandular and stromal differentiation in the mid-luteal phase. These findings suggest a profound modification of luteal endometrial development in stimulated cycles. This hypothesis is further supported by the demonstration of a modified endometrial steroid receptor regulation and a profound antiproliferative effect in IVF cycles. The time of maximal endometrial receptivity is defined as the implantation window and is characterized by the expression of various endometrial products, among which pinopodes, integrins and leukaemia inhibitory factor are best described. Premature expression of pinopodes and integrins are in line with the observation of precocious luteal transformation following ovarian stimulation, although the clinical relevance with respect to the establishment of a clinical pregnancy awaits further validation. Studies exploring the endometrium within the cycle of embryo transfer have shown a deleterious effect of severe peri-ovulatory maturation advancement exceeding 3 days, as no clinical pregnancies were obtained in this condition. Further unravelling of molecules involved in the implantation mechanism is needed for a better comprehension of the link between altered endometrial development and receptivity in IVF cycles.

中文翻译：

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体外受精刺激周期的子宫内膜。

已知IVF的卵巢刺激会影响黄体期功能。因此，IVF周期中的子宫内膜会受到内分泌环境的改变，并可能受到卵巢刺激疗法的直接影响。在这种循环中影响子宫内膜接受性的因素了解甚少。将IVF周期的子宫内膜与自然周期作为对照进行比较的研究表明，IVF周期的排卵后和黄体早期阶段的分泌物发生过早的变化，随后在黄体中期阶段出现了大部分不同步的腺体和基质分化。这些发现表明在刺激周期中黄体子宫内膜发育的深刻改变。该假说进一步得到证实，证明了修饰的子宫内膜类固醇受体调节作用和在IVF周期中具有深远的抗增殖作用。子宫内膜的最大接受时间定义为植入窗口，其特征在于各种子宫内膜产物的表达，其中最好描述了pinopodes，整合素和白血病抑制因子。品柱和整联蛋白的过早表达与卵巢刺激后早熟的黄体转化的观察一致，尽管与建立临床妊娠的临床相关性尚待进一步验证。探索胚胎移植周期内的子宫内膜的研究表明，严重排卵期成熟超过3天会产生有害影响，因为在这种情况下没有临床妊娠。为了更好地理解IVF周期中子宫内膜发育变化和接受性之间的联系，需要进一步弄清楚植入机制中涉及的分子。