Petousis S, et al. - In this prospective observational study, researchers compared endometrial expression of total progesterone receptors’ PR(A + B) and type-B receptors’ (PR-B) between all categories of infertile and fruitful controls in order to ascertain the endometrial expression of progesterone receptors in various subgroups of infertile women (those with tubal factor, ovarian failure, endometriosis or unexplained infertility) during implantation window. Women with unexplained infertility were found to have impaired endometrial expression of progesterone receptors. The final reproductive outcome may be significantly impacted by implementing therapeutic strategies targeting on improving progesterone receptors’ expression.