Cumulative pregnancy rates resulting from the use of fresh and frozen oocytes: 7 years’ experience

Storing supernumerary embryos and transferring them later fully utilizes the reproductive potential of retrieved oocytes, allowing a significant increase in the overall number of pregnancies achieved from a single cycle of ovarian stimulation treatment. As an alternative to embryo cryopreservation, preservation of unfertilized oocytes has been proposed to maximize clinical outcome. This paper presents data concerning the cumulative pregnancy rate after use of fresh and cryopreserved oocytes. In 80 treatment cycles in which patients chose to have only a few fresh oocytes inseminated, 24 pregnancies were obtained (30.0%), with an implantation rate of 22.6%. After cryopreservation with the standard slow-cooling protocol, the survival, fertilization and cleavage rates of 918 frozen oocytes were 43.4, 51.5 and 86.0% respectively. A total of 14 frozen pregnancies were achieved, with pregnancy rate 19.2% per transfer and implantation rate 12.3%. The cumulative pregnancy rate was 47.5% per patient. Therefore, despite a low rate of oocyte post-thaw survival, it appears that oocyte storage appreciably improves the number of pregnancies per treatment cycle in cases in which only a minority of oocytes are destined for the fresh treatment. This outcome provides valuable information for appraising the chances of clinical success when the option of embryo cryopreservation is not available.