AbstractIntroductionThe menstrual cycle is regulated by a complex interplay between endometrial epithelial cells, endothelial cells, immune cells, and sex hormones. To communicate, cells secrete cytokines that have multiple and diverse effects on recipient cells. Knowledge of how these cells interact in the uterus is insufficient. Menstrual blood is easily accessible and provides a source to study menstrual cycle physiology. This study aimed to determine the cytokine profile in menstrual blood plasma and investigate the differences in cytokine profiles between menstrual and peripheral blood plasma. Several previous studies indicate an improved chance of embryo implantation after endometrial scratching. Consequently, our secondary aim was to compare the menstrual blood cytokine profile before and after luteal phase endometrial scratching.Material and methodsNineteen healthy donors collected menstrual blood for the first 24 hours of menstruation in two sequential cycles. Matched peripheral blood was taken at the same time. An endometrial biopsy was performed at cycle day 7‐9 post ovulation in between the two collection times. A Luminex multiplex assay was performed in one batch analyzing a predetermined group of cytokines in plasma.ResultsPeripheral blood plasma and menstrual blood plasma showed substantial significant differences in cytokine profile. In menstrual blood plasma, C5/C5a, interleukin‐6 (IL‐6), IL‐1β, and CXCL8 were detected in high concentrations, whereas IL‐2, IL‐12p70, XCL1/Lymphotactin, and interferon‐γ were low. The most pronounced median differences between menstrual and peripheral blood plasma were found for IL‐6, IL‐1β, and CXCL8. The cytokine profiles of menstrual blood plasma were similar between the individual donors and did not differ over two subsequent cycles. None of the cytokines analyzed in menstrual blood plasma differed significantly before or after luteal phase endometrial scratching (P < .01).ConclusionsOur results demonstrate that the menstrual blood cytokine profile is distinctly different from peripheral blood plasma and that the inter‐individual difference in menstrual blood cytokine profile in healthy donors is limited and stable over time. The small injury caused by an endometrial biopsy does not change the cytokine profile in the subsequent menstrual cycle. Our study provides new insights into menstrual cycle physiology.