Duration of cryopreservation does not negatively affect human embryo post-thaw survival and implantation

Abstract

OBJECTIVE: To determine the effect of duration of cryopreservation on the survival and implantation rate of thawed day 3 (multi-cellular) embryos.DESIGN: Retrospective cohort analysis in a private In Vitro Fertilization (IVF) practice.MATERIALS AND METHODS: All autologous Frozen Embryo Transfer (FET) cycles performed between 2003 and 2007 were extracted from the embryology database of a large private IVF practice. A total of 808 thaw/transfer cycles were identified, with a total of 3535 thawed Day 3 embryos. The post-thaw survival and implantation rates of these embryos and the corresponding clinical pregnancy rates from their transfers were evaluated, and these data were stratified according to the length of time the embryos were in cryogenic storage. Embryos were cryopreserved using the standard 1,2 propanediol and 0.1M sucrose method on Day 3 post-insemination utilizing a Cryologic (CL863) freezer. Embryo thawing was achieved through stepwise dilutions of propanediol and sucrose at room temperature. An embryo was considered to have survived cryopreservation and thawing when greater than or equal to 50% of the pre-freeze blastomeres are intact in the post-thaw embryo. Transfers were performed in controlled hormone replacement cycles with endometrial preparation by step-up oral estradiol dosing in the follicular phase and intra-muscular progesterone in the luteal phase.Table 1Effect of duration of cryopreservation on survival, implantation and clinical pregnancy/transfer ratesDuration of storage (years)0-11+ to 22+ to 33+ to 4>4p value% Survival rate (# embryos survived/# embryos thawed52.7 (1194/2267)48.5 (288/594)52.0 (262/504)56.5 (70/124)67.4 (31/46)0.3% Implantation rate (# sacs/# embryos transferred24.7 (225/912)29.3 (66/225)25.3 (56/221)21.7 (13/60)29.2 (7/24)0.8% Clinical pregnancy rate (# clinical pregnancies/# embryo transfers35.6 (171/480)40.1 (55/137)34.1 (46/135)26.2 (11/42)46.2 (6/13)0.5 Open table in a new tab CONCLUSIONS: The duration of embryo cryopreservation does not affect embryo survival, embryo implantation or clinical pregnancy rate per embryo transfer. These data may be useful in reassuring patients that the implantation potential of embryos is conserved when embryos are maintained carefully in cryopreserved storage, and offer evidence supporting the safety of cryogenic storage of human embryos within the time interval considered in this analysis. OBJECTIVE: To determine the effect of duration of cryopreservation on the survival and implantation rate of thawed day 3 (multi-cellular) embryos. DESIGN: Retrospective cohort analysis in a private In Vitro Fertilization (IVF) practice. MATERIALS AND METHODS: All autologous Frozen Embryo Transfer (FET) cycles performed between 2003 and 2007 were extracted from the embryology database of a large private IVF practice. A total of 808 thaw/transfer cycles were identified, with a total of 3535 thawed Day 3 embryos. The post-thaw survival and implantation rates of these embryos and the corresponding clinical pregnancy rates from their transfers were evaluated, and these data were stratified according to the length of time the embryos were in cryogenic storage. Embryos were cryopreserved using the standard 1,2 propanediol and 0.1M sucrose method on Day 3 post-insemination utilizing a Cryologic (CL863) freezer. Embryo thawing was achieved through stepwise dilutions of propanediol and sucrose at room temperature. An embryo was considered to have survived cryopreservation and thawing when greater than or equal to 50% of the pre-freeze blastomeres are intact in the post-thaw embryo. Transfers were performed in controlled hormone replacement cycles with endometrial preparation by step-up oral estradiol dosing in the follicular phase and intra-muscular progesterone in the luteal phase. CONCLUSIONS: The duration of embryo cryopreservation does not affect embryo survival, embryo implantation or clinical pregnancy rate per embryo transfer. These data may be useful in reassuring patients that the implantation potential of embryos is conserved when embryos are maintained carefully in cryopreserved storage, and offer evidence supporting the safety of cryogenic storage of human embryos within the time interval considered in this analysis.