3. To compare the BAP-EB attachment rate and expression of the attachment-related "receptive" EEC surface molecules between pre-receptive and receptive endometrium and between women with repeated implantation failure (RIF) and subfertile women due to male factors. To identify women with endometrial defects, women with RIF and failed IVF after preimplantation genetic screening (PGS) will be recruited. The latter recruitment criterion excludes RIF due to embryo aneuploidy.