Two of a kind? Immunological and clinical risk factors differ between recurrent implantation failure and recurrent miscarriage

•Elevation of antinuclear antibodies and intrauterine adhesions are more prevalent in RM.•Patients with RIF show a higher rate of submucous fibroids and factor VIII elevation.•The prevalence of antiphospholipid syndrome was low and not different between groups.•Lower Tregs in RM and higher uNK cells in RIF suggest a different immune profile.•Subsuming RM and RIF in one group should be avoided. Recurrent miscarriage (RM) and recurrent implantation failure (RIF) are unsolved challenges in reproductive medicine. Whether RIF patients share the same risk factors as RM patients is a matter of debate. Besides clinical factors, immune alterations are discussed in both conditions. The scope of this study was to compare the prevalence of clinical and immunological risk factors in a large cohort of RM and RIF patients. Between 11/2011 and 02/2019, 613 RM and 185 RIF patients were included. A screening for anatomical malformations, endocrine, autoimmune, prothrombotic and parental chromosomal disorders was performed. The immune status was assessed using flow cytometry analysis of peripheral lymphocyte subpopulations and uterine natural killer cells (uNK cells) using immunohistochemistry. RM patients showed a higher rate of intrauterine adhesions and elevated antinuclear antibodies ≥ 1:160 (p