The purpose of this study is to evaluate the role of DHEA in counteracting the effects of ovarian ageing in an in-vitro fertilization (IVF) model. The study will examine whether the use of DHEA could improve clinical pregnancy rates following IVF treatment in women predicted to have aged ovaries by increasing oocyte quantity (ovarian response to gonadotrophins) and/ or by improving oocyte quality. The oocyte quality will be assessed by morphological and molecular markers.