This is a prospective cross-over study. Investigators want to study the effect of different dosages of recombinant FSH in the same patient on the expression of the FSH- and LH-receptors in the granulosa cells and on the endocrine milieu in the blood and the follicular fluid. An improved understanding of the mechanism leading to progesterone elevation might initiate a change in the ovarian stimulation approach, thereby not only preventing progesterone elevation and its negative consequences on ART (Assisted Reproductive Technology) outcome, but also improving individualization of the ovarian stimulation treatment according to the patients' characteristics.
To study the influence of different daily rec-FSH dosages (150 IU versus 300 IU), performed in the same patient in consecutive cycles, on the relation between FSH- and LH-receptors of the granulosa cells of the growing follicle.