The clinical significance of the retrieval of a low number of oocytes following mild ovarian stimulation for IVF: a meta-analysis

BACKGROUND: Milder ovarian stimulation protocols for in vitro fertilization(IVF) are being developed to minimize adverse effects. Mildstimulation regimens result in a decreased number of oocytesat retrieval. After conventional ovarian stimulation for IVF,a low number of oocytes are believed to represent poor ovarianreserve resulting in reduced success rates. Recent studies suggestthat a similar response following mild stimulation is associatedwith better outcomes. METHODS: This review investigates whether the retrieval of a low numberof oocytes following mild ovarian stimulation is associatedwith impaired implantation rates. Three randomized controlledtrials comparing the efficacy of the mild ovarian stimulationregimen (involving midfollicular phase initiation of FSH andGnRH co-treatment) for IVF with a conventional long GnRH agonistco-treatment stimulation protocol could be identified by meansof a systematic literature search. RESULTS: These studies comprised a total of 592 first treatment cycles.Individual patient data analysis showed that the mild stimulationprotocol results in a significant reduction of retrieved oocytescompared with conventional ovarian stimulation (median 6 versus9, respectively, P < 0.001). Optimal embryo implantationrates were observed with 5 oocytes retrieved following mildstimulation (31%) versus 10 oocytes following conventional stimulation(29%) (P = 0.045). CONCLUSIONS: The optimal number of retrieved oocytes depends on the ovarianstimulation regimen. After mild ovarian stimulation, a modestnumber of oocytes is associated with optimal implantation ratesand does not reflect a poor ovarian response. Therefore, thefear of reducing the number of oocytes retrieved following mildovarian stimulation appears to be unjustified.