Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.

A vast array of successive epigenetic modifications ensures the creation of a healthy individual. Crucial epigenetic reprogramming events occur during germ cell development and early embryogenesis in mammals. As highlighted by the large offspring syndrome with in vitro conceived ovine and bovine animals, any disturbance during germ cell development or early embryogenesis has the potential to alter epigenetic reprogramming. Therefore the complete array of human assisted reproductive technology (ART), starting from ovarian hormonal stimulation to embryo uterine transfer, could have a profound impact on the epigenetic state of human in vitro produced individuals. Although some investigators have suggested an increased incidence of epigenetic abnormalities in in vitro conceived children, other researchers have refuted these allegations. To date, multiple reasons can be hypothesized why irrefutable epigenetic alterations as a result of ART have not been demonstrated yet.

No abstract