OBJECTIVE: To evaluate the extent to which transfers of frozen single embryos increase cumulative pregnancy rates. DESIGN: Retrospective analysis. SETTING: IVF unit of a university hospital. PATIENT(S): Patients undergoing IVF cycles that were carried out from 2001 to 2005 (n = 1758). Patients were assigned to three groups according to the number of embryos frozen: group A, no cryopreservation; group B, a single embryo frozen; group C, several embryos frozen. INTERVENTION(S): Analysis of fresh ETs as a function of the number of embryos frozen and comparison outcomes for the thawing of a single embryo between subgroups B* (only one embryo frozen and thawed) and C* (last embryo of the cohort thawed). MAIN OUTCOME MEASURE(S): Implantation and pregnancy rates after fresh ETs and embryo survival and pregnancy rates after the transfer of a single thawed embryo. RESULT(S): The pregnancy rate per fresh ET increased significantly with the number of embryos frozen: 16.2% in group A, 21.4% in group B, and 26.5% in group C. For single thawed embryos, survival was higher in group C* (91.7%) than in group B* (72.6%). The pregnancy rate was also significantly higher in group C* (19.4% vs. 0%). CONCLUSION(S): The freezing of single embryos is of no benefit in cumulative pregnancy rates. ET strategies should therefore be reviewed.
OBJECTIVE: To evaluate the extent to which transfers of frozen single embryos increase cumulative pregnancy rates. DESIGN: Retrospective analysis. SETTING:IVF unit of a university hospital. PATIENT(S): Patients undergoing IVF cycles that were carried out from 2001 to 2005 (n = 1758). Patients were assigned to three groups according to the number of embryos frozen: group A, no cryopreservation; group B, a single embryo frozen; group C, several embryos frozen. INTERVENTION(S): Analysis of fresh ETs as a function of the number of embryos frozen and comparison outcomes for the thawing of a single embryo between subgroups B* (only one embryo frozen and thawed) and C* (last embryo of the cohort thawed). MAIN OUTCOME MEASURE(S): Implantation and pregnancy rates after fresh ETs and embryo survival and pregnancy rates after the transfer of a single thawed embryo. RESULT(S): The pregnancy rate per fresh ET increased significantly with the number of embryos frozen: 16.2% in group A, 21.4% in group B, and 26.5% in group C. For single thawed embryos, survival was higher in group C* (91.7%) than in group B* (72.6%). The pregnancy rate was also significantly higher in group C* (19.4% vs. 0%). CONCLUSION(S): The freezing of single embryos is of no benefit in cumulative pregnancy rates. ET strategies should therefore be reviewed.