- Objective To study whether an injury-induced inflammation might be the mechanism underlying the favorable effect of endometrial biopsy on the implantation rate in in vitro fertilization (IVF) patients. Design Controlled clinical study. Setting A medical center IVF unit and a research institute. Patient(s) Women undergoing IVF who had previous failed treatment cycles. Intervention(s) Endometrial samples were collected from two groups of patients on day 21 of their spontaneous menstrual cycle. The experimental, but not the control group underwent prior biopsy treatment on days 8 or/and 11 to 13 of that same cycle. Main Outcome Measure(s) Abundance of immune cells, cytokines/chemokines level, correlation between these parameters and pregnancy outcome. Result(s) A statistically significantly higher amount of macrophages/dendritic cells (HLA-DR + CD11c + cells) and elevated proinflammatory cytokines, tumor necrosis factor-α (TNF-α), growth-regulated oncogene-α (GRO-α), interleukin-15 (IL-15), and macrophage inflammatory protein 1B (MIP-1B), were detected in day-21 endometrial samples of the experimental group. A direct stimulatory effect of TNF-α on MIP-1B, GRO-α, and IL-15 messenger RNA (mRNA) expression was demonstrated. A positive correlation was found between the levels of macrophages/dendritic cells, MIP-1B expression, and TNF-α expression and the pregnancy outcome. Conclusion(s) A biopsy-induced inflammatory response may facilitate the preparation of the endometrium for implantation. Increased MIP-1B expression could possibly serve for prediction of implantation competence.