ABSTRACT
The human endometrium is not receptive to embryos throughout most of the menstrual cycle. The endometrium acquires the ability to permit the developing embryo to implant between days 5-10 after ovulation. This temporal window in the secretory phase of the menstrual cycle is called the “implantation window.” During this period the endometrium undergoes structural and functional changes induced by ovarian steroids namely estrogens and progesterone. These steroids alter the endometrium and prepare it to be receptive to invasion by the embryo.
