The prognostic value of uNK cell count and histological dating in the mid-luteal phase of women with reproductive failure

Objective: Histological dating has been used for decades to evaluate the histological maturation of the endometrium. Uterine natural killer cells are thought to play a significant role in pregnancy. While several studies have shown an increased number of uNK cells in women with recurrent reproductive failure, its prognostic value of pregnancy outcome remains uncertain. The aim of this study was to determine whether or not the prognostic value of uNK measurement on pregnancy outcome is improved when it is combined with histological dating of the same endometrial specimen. Study design: This is a retrospective study. Histological dating and uNK cell count was performed on endometrial biopsies taken from women with either recurrent miscarriage (RM, n = 94) or recurrent implantation failure (RIF, n = 72). Women who conceived within a year of the biopsy (n = 83) were included in a further analysis to examine the prognostic value of uNK cell count and histological dating on the outcome of a subsequent pregnancy. Results: There was a significant (p = 0.01) association between uNK cells and histological dating; retarded endometrium was less likely to have a high uNK cell count (16/58, 28%) than normally developed endometrium (52/108, 48%). Whilst uNK cell count on its own did not have a significant correlation to the pregnancy outcome, a retarded endometrium is significantly (p = 0.01) associated with a higher miscarriage rate (68%, 13/19) than normally developed endometrium (35%, 23/64) in women with reproductive failure. Regardless of the result of uNK cell count (normal or abnormal), combining the results of histological dating appeared to have significantly improved the prognostic value. Conclusions: We found that the prognostic value of uNK cell count is significantly increased when the result is combined with histological dating, primarily because histological dating is significantly correlated with pregnancy outcome.