Endometrial biopsy Two endometrial biopsies were performed during a single menstrual cycle in each subject. The early biopsy was performed on the pre-ovulatory day (late follicle phase) and the endometrial tissues were collected from the anterior wall of the uterine cavity. Whereas the late biopsy was performed on ovulation day +7 (midluteal phase or implantation widow phase), and the endometrial sample was collected from the posterior wall of the uterine cavity with or without dilatation of the cervix by using an endometrial curette (#4164 prebet, Genetics, pommel, Belgium). Each sample was divided into three pieces and immediately fixed. Samples for scanning electron microscopy for fixed in a solution containing 2.5% (wt/vol) glutaraldehyde, 0.5% paraformaldehyde, 0.1 mol/L of sucrose, 0.1 mol/L of sodiumcacodylate, and 3 mmol/L of calciumchloride (pH, 7.4). Samples for immunohistochemistry were fixed in 4% formalin . Samples for transmission electron microscopy was fixed by 2.5% glutaraldehyde arsenate ;