 - Three groups of patients will be enrolled: 10 fertile controls C1-10: women who are participating in the donor egg program as egg donors, 10 with unexplained implantation failure IF1-10: patients who have failed IVF cycles -failure of implantation following 2 or more cycles with transfer of embryos of good quality-at least 2 cleaving embryos with 6-8 cells, grades 1- 3 scale 1-highest and 5-poorest morphology score, and normal uterus, and 10 with recurrent unexplained first trimester miscarriages RM1-10: 2 consecutive miscarriages under 10 weeks, after spontaneous or IVF conceptions. 