Background: The aim of the present study is to investigate cryopreservation of oocytes in patients refusing embryo cryopreservation for ethical reasons, patients from whom no sperm could be retrieved and patients with enough oocytes to yield a number of fresh and cryopreserved embryos to transfer.
Methods: A total of 2900 oocytes out of 6216 retrieved were cryopreserved in 286 patients undergoing 303 cycles. The reasons for cryopreservation were because no sperm was found in 16 cycles, for ethical or personal reasons in 80, and in 207 only supernumerary oocytes were frozen. In 159 cycles, the oocytes were thawed and the surviving metaphase II oocytes microinjected.
Results: A total of 1087 oocytes were thawed, 760 (69.9%) survived and 687 were microinjected. We obtained 368 (53.5%) normally cleaved embryos, 331 were transferred and 37 were cryopreserved. One hundred and forty-five transfers (range 1-3 embryos/patient) were performed and 18 (12.4%) pregnancies were obtained. Twelve patients delivered 13 healthy children, and six first trimester abortions were observed (33.3%).
Conclusion: Although a low implantation rate was observed and a higher abortion rate than in fresh cycles, our results show that in sibling oocytes, the process of cryopreservation apparently does not affect the fertilization and cleavage rate. In this group of patients, producing a large number of mature gametes, oocyte cryopreservation gives the couple extra chances to achieve a pregnancy within a single retrieval and is a good effort towards reducing the number of embryos cryopreserved and enhancing our experience in this new technology.