Scheduling the initiation of ovarian stimulation in a gonadotrophin-releasing hormone (GnRH)-antagonist protocol by sex steroid pretreatment has been suggested as a means to reduce the incidence of oocyte retrievals during weekends. The rationale is that by manipulating the initiation of gonadotrophin stimulation, Thursday or Friday will be avoided as days on which triggering of final oocyte maturation will be performed and thus weekend oocyte retrievals will not occur. Apparently, the assumption behind such an approach is that duration of stimulation is homogenous enough to serve this purpose reliably. However, existing data suggest that large inter-individual variation exists in the duration of gonadotrophin stimulation required to reach predefined criteria for triggering final oocyte maturation, regardless of whether stimulation was initiated with spontaneous menstruation or after pretreatment with sex-steroids. Therefore, it is highly unlikely that any type of pretreatment aiming to allow initiation of stimulation on a certain day will result in avoidance of weekend oocyte retrievals, when predefined criteria for triggering final oocyte maturation are used.