Implantation is a critical step in human reproduction. The success of this step is dependent on a competent blastocyst, receptive endometrium, and successful cross talk between the embryonic and maternal interfaces. Recurrent implantation failure is the lack of implantation after the transfer of several embryo transfers. As the success of in vitro fertilization has increased and failures have become more unacceptable for patients and providers, the literature on recurrent implantation failure has increased. While this clinical phenomenon is often encountered, there is not a universally agreed-on definition—something addressed in an earlier portion of this Views and Reviews.

Implantation failure can result from several different factors. In this review, we discuss factors including the maternal immune system, genetics of the embryo and parents, anatomic factors, hematologic factors, reproductive tract microbiome, and endocrine milieu, which factors into embryo and endometrial synchrony. These potential causes are at various stages of research and not all have clear implications or immediately apparent treatment.

植入是人类生殖的关键步骤。这一步的成功取决于一个称职的囊胚、接受性子宫内膜以及胚胎和母体界面之间的成功串扰。复发性植入失败是指多次胚胎移植后没有植入。随着体外受精成功率的增加和失败对患者和提供者来说变得更加不可接受，关于复发性植入失败的文献增加了。虽然经常遇到这种临床现象，但并没有一个普遍认可的定义——在本《意见和评论》的前面部分中已经解决了这个问题。

植入失败可能由几个不同的因素造成。在这篇综述中，我们讨论了影响胚胎和子宫内膜同步性的因素，包括母体免疫系统、胚胎和父母的遗传学、解剖学因素、血液学因素、生殖道微生物组和内分泌环境。这些潜在原因处于不同的研究阶段，并非都具有明确的含义或立即明显的治疗方法。