New strategies of ovarian stimulation based on the concept of ovarian follicular waves: From conventional to random and double stimulation.

The theory of a multicyclic development of follicles during the menstrual cycle prompted new approaches to ovarian stimulation, such as starting gonadotrophins for ovarian stimulation at any time during the menstrual cycle or using double stimulation during it, with stimulation in both the follicular and luteal phases. Because of the asynchrony between endometrial receptivity and embryo development with a 'non-conventional start' stimulation, all the oocytes/embryos are generally cryopreserved and transferred subsequently. This deferred transfer policy is currently possible given the advances in vitrification techniques, with success rates comparable to those following transfer with 'fresh' embryos. New stimulation approaches, together with advanced cryopreservation techniques, allow for a total 'disarticulation' between the time of the menstrual cycle, ovarian stimulation start and embryo transfer. This new approach to ovarian stimulation is particularly useful for women seeking fertility preservation, especially where a shortened time to starting cancer treatment is desirable. Also, poor responders could benefit from the new stimulation protocols by continuing ovarian stimulation after the first oocyte retrieval, thereby obtaining more oocytes or embryos compared with the conventional approach.