Prognostic value of the measurement of uterine natural killer cells in the endometrium of women with recurrent miscarriage

BACKGROUND: Studies in mice suggest that CD56+ uterine natural killer (uNK) cells play an important role in implantation. Studies in humans have described an increase in the number of uNK cells in the non-pregnant midsecretory endometrium of women with unexplained recurrent miscarriage (RM). However, the predictive value of uNK cell number in the maintenance of pregnancy is controversial. METHODS: A blind retrospective study was undertaken. The percentage of stromal cells positive for CD56 was identified by inummocytochemistry in endometrial biopsies from 10 normal control women and 87 women with unexplained RM, of whom 51 became pregnant following biopsy. Biopsies were obtained on days LH + 7 to LH + 9. RESULTS: As in previous studies, the number of uNK cells in the 87 women with RM (mean 11.2% range 1.1-41.4%) was significantly higher (P = 0.013) than in the control women (mean 6.2% range 2.2-13.9%). No significance difference in uNK numbers was observed between 19 women who miscarried (mean 9.6% range 1.7-25.0%) and 32 women who had a live birth (mean 13.3% range 1.1-41.4%) in a subsequent pregnancy. CONCLUSIONS: In this study numbers of uNK cells in the peri-implantation endometrium of women with unexplained recurrent miscarriage did not predict subsequent pregnancy outcome.