The human endometrium is an anatomic and functional requirement for species continuation. With rare exception, the endometrium is the sole location for successful implantation, placentation, and growth and survival of the conceptus until birth. Despite this outsized relevance, this tissue has always been seen as the ugly mucosa of a "nonvital" organ responsible for menstruation a fairly unpopular event.1 Consequently, research into the endometrium has received far less support than research into the brain, heart, or even placenta. This phenomenon also holds true in the clinic. Since the inception of reproductive medicine, the maternal endometrium has been considered a passive part of the reproductive process; a "good embryo" was all that mattered. This view requires revision given that the efficacy of in vitro fertilization remains low despite considerable improvements in embryology and embryo transfer technologies in recent decades. Furthermore, endometrial decidualization deficiency has been suggested as a contributing factor for the pathogenesis of pregnancy disorders with particular attention to severe preeclampsia.
