Hopes and facts about mild ovarian stimulation.

Over the last two decades, easier and less expensive stimulation treatments have been largely replaced by more complex and more demanding protocols. Since the mid-nineties, long-term gonadotrophin-releasing hormone agonist stimulation protocols have been widely used. Such lengthy expensive regimens are not free from short- and long-term risks and complications. Mild stimulation protocols reduce the mean number of days of stimulation, the total amount of gonadotrophins used and the mean number of oocytes retrieved. The proportion of high quality and euploid embryos seems to be higher compared with conventional stimulation protocols and the pregnancy rate per embryo transfer is comparable. Moreover, the reduced costs, the better tolerability for patients and the less time needed to complete an IVF cycle make mild approaches clinically and cost-effective over a given period of time. However, further prospective randomized studies are needed to compare cumulative pregnancy rates between the two protocols. Natural cycle IVF, with minimal stimulation, has been recently proposed as an alternative to conventional stimulation protocols in normo- and poor responder patients. Although acceptable results have been reported, further large prospective randomized studies are needed to better evaluate the efficacy of these minimal regimens compared with conventional stimulation approaches.