The observer and cycle-to-cycle variability in the measurement of uterine natural killer cells by immunohistochemistry.

The aim of the study was to investigate the various potential sources of variability of counting endometrial uNK cells by immunohistochemistry. Precisely timed endometrial biopsy samples were obtained from women suffering from recurrent miscarriage or recurrent implantation failure (RIF) after IVF on days LH+7-LH+9 of the cycle. uNK cells in wax embedded sections were immunostained for CD56+ and expressed as a percentage of total stromal cells.