The role of tacrolimus in women with unexplained infertility: A narrative review

Several autoimmune and immunological disorders can cause infertility. About 10-20% of infertility cases are related to fetal-maternal immune factors. The use of immunological treatments in women with infertility is an emerging strategy. Tacrolimus, a calcineurin inhibitor, has been shown in some studies to prevent fetal rejection and promote tolerance by inhibiting activated natural killer cells, natural killer T cells, and macrophages. In this review, we will evaluate the effects of tacrolimus on recurrent pregnancy loss and assisted reproductive technology failure. The search strategy for relevant articles was conducted in PubMed, Scopus, Google Scholar, and Web of Science databases using MeSH terms and keywords including Tacrolimus [mh], FK506, infertility [mh], abortion, spontaneous [mh], recurrent miscarriage, recurrent pregnancy loss, and recurrent implantation failure. We sought the most recent and reliable studies in the field of infertility. Tacrolimus is relatively safe and effective during pregnancy, with no major fetal-maternal complications. It is beneficial for with an elevated T helper-1/T helper-2 cell ratio. However, more studies should be designed to clarify the optimal dosage, treatment duration, and timing of initiation and cessation of tacrolimus to maximize its safety and efficacy during pregnancy.