Do uterine natural killer cell numbers in peri-implantation endometrium predict hypertensive disorder in pregnancy in women with a history of reproductive failure?

• We studied the association between uNK cells and hypertensive disorder in pregnancy.
• Endometrial uNK cells counts were measured during the peri-implantation period.
• Although women with high uNK cell counts had twice the incidence of hypertensive disease as women with normal uNK cell numbers, this finding was not statistically significant.
• The activity of uNK cells may be a better predictor of hypertensive disease.

The aim of this study was to investigate whether or not increased uterine natural killer (uNK) cell numbers in the peri-implantation endometrium are associated with an increased risk of hypertensive disorders in a subsequent pregnancy. This is a retrospective study including 80 women with a history of unexplained recurrent miscarriage or recurrent implantation failure. Precisely timed endometrial biopsies were obtained from women 7–9 days after the luteinising hormone surge. uNK cells were immunostained for CD56+ and expressed as a percentage of total stromal cells. Patients were defined as having a high uNK cell count if the percentage of total stromal cells was more than 13.9%. Five out of 29 (17.2%) women in the high uNK cell count group and 5 out of 51 (9.8%) women in the normal uNK cell count group developed gestational hypertension. Pre-eclampsia was diagnosed in 2 (6.9%) patients in the high uNK cell count group and 1 (2.0%) patient from the normal uNK cell count group. There was no significant difference in the incidence of either gestational hypertension (P = 0.483) and pre-eclampsia (P = 0.296) between groups. The overall incidence of hypertensive disease in women with high uNK cell count (24.1%) was two times higher than women with normal uNK cell count (11.8%), but it was not statistically significant (P = 0.208). An increased uNK cells count in the peri-implantation period in a cycle prior to conception did not appear to significantly increase the likelihood of hypertensive disease of pregnancy.