Recent developments in reproductive medicine address oocyte morphology, sperm analysis and embryo selection. However, in a subgroup of infertile couples, it is the embryo implantation process that is disrupted. Diagnostic tools to identify patients at risk of implantation failure are limited and therapeutic options are far away from being established. In this review we focus on selected possible causes and treatments of failed implantation. Reproductive surgery allows a proper first step diagnosis and therapy of recurrent implantation failure (RIF). Possible anatomical malformations and associated diseases with treatment options are mentioned. Diagnostic procedures in patients often focus on defining gene polymorphisms (like hereditary thrombophilia and p53) and determinants of endometrial receptivity including endometrial gene expression profiles. Although significant differences in gene expression have been identified, the study populations are quite small, some of the data conflicting and clinical significance has yet to be proven. Implantation requires a close interaction between the fetal trophoblast and the maternal endometrium with natural killer cells (NK cells) playing a main part at the feto-maternal interface during early pregnancy. Therefore this review also focuses on NK cell receptor expression and new immunomodulatory treatment options like G-CSF in RIF patients.
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