Allocating a minimum of 4 metaphase II oocytes has good reproductive outcome in a shared egg donor program

Abstract

OBJECTIVE: To analyze if there is any ideal minimum number of oocytes to be allocated to each recipient, in a shared egg donor program. DESIGN: Retrospective cohort study. MATERIALS AND METHODS: In 2006-2008, 836 women received oocytes in our shared egg donor program. We allocate a minimum of 4 metaphase II (MII) oocytes to each one. The final number was determined by the number of MII oocytes retrieved from the donor. We divided the cohort according to the number of MII oocytes received (Groups A:4; B:5; C:6; D:7; E:≥8 MII oocytes). Our hypothesis was that the greater the number of MII oocytes received, the higher the pregnancy rate achieved. We used chi square test to analyze the data. The sample size was calculated to have alpha and beta errors at 5% and 20% respectively, to find a duplication of the pregnancy rate between the higher and the lower strata. RESULTS: A total of 333 oocyte donors' cycles and 836 fresh embryo transfers in recipients were evaluated. A media of 5.4 MII oocytes were allocated to each recipient, with a ratio recipient/donor of 2.6. A higher proportion of top quality transferred embryos was seen in recipients that received 7 or more MII oocytes (85% vs 70% of the transfers, p<0.05). No statistically significant differences were found in implantation, clinical pregnancy (group A:42.7%; B:46.6%; C:50%; D:46.3%, E:52.9%; p=NS) and miscarriage rates. A statistically significant difference was found in embryo freezing rate when recipients received a larger number of MII oocytes (group A:8.5%; B:18.1%; C:19.2%; D:41.0%, E:48.8%; p<0.001). CONCLUSIONS: Allocating a minimum of 4 MII oocytes per recipient offers a satisfactory reproductive outcome in a shared egg donor program. After a large sample was analyzed, our hypothesis has been rejected, suggesting that no relevant differences exist among strata. However, the accumulated pregnancy rate may be higher among those patients with frozen embryos. This study adds a significant body of evidence to support the development of shared oocytes donor programs.