Embryo implantation is a complex process; primary step in implantation is the initiation of
dialogue between free floating blastocyst and the receptive endometrium. This is followed by a stable
adhesion of the blastocyst anchors to the endometrial basal lamina and stromal extracellular matrix. The last
step is invasion of the embryo through the luminal epithelium and its basal lamina into the uterine stroma.
Successful embryo implantation depends up on number of factors like steroid hormones (progesterone,
estrogen), Cyclooxygenases, prostaglandins, cytokines, growth factors, transcription factors (HOXA-10 and
HOXA-11), and adhesion molecules (integrins, selectins, cadherins, mucins) and receptive endometrium.
Importantly, there is timely regulation of these factors and their cross talk which mediates the implantation
process. Blastocyst is unable to implant successfully if there is deregulation in any of these factors leading to
pregnancy loss. In this chapter we reviewed the information available till date to provide possible causes of
implantation failure and its positive outcomes.
Keywords: Implantation, endometrial receptivity, growth factors, cytokines, hormones, adhesion molecules.
