Introduction: Examining the many potential reasons why euploid blastocysts do not always result in viable pregnancies...

To result in a viable delivery: 1) a capable embryo must be accurately deposited and retained in an optimal location of the uterine cavity; 2) the endometrium must be receptive and synchronized to the developmental stage of the embryo; 3) the uterus must be physiologically and anatomically adequate; and 4) there should not be the presence of circulating factors capable of disrupting normal implantation and placentation, nor the absence of specific factors required for endometrial receptivity. The intricate interaction between the embryo and the uterus is discussed in this series of reviews.