Unexplained recurrent miscarriage (uRM) is defined as two or more spontaneous abortions prior to 20 weeks of gestation with unknown etiology. Peripheral blood natural killer (pNK) cells contact with the villus and exert important role in normal pregnancy. However, it is still controversial about the association between pNK cytotoxicity and uRM, and the underlying mechanism remains unknown so far.

中文翻译：

---

外周血NK细胞的低细胞毒活性可能与原因不明的复发性流产有关

不明原因的复发性流产 (uRM) 被定义为在妊娠 20 周之前两次或两次以上的不明原因的自然流产。外周血自然杀伤 (pNK) 细胞与绒毛接触并在正常妊娠中发挥重要作用。然而，pNK细胞毒性与uRM之间的关联仍存在争议，其潜在机制至今仍不清楚。