Repeated cryopreservation process impairs embryo implantation potential but does not affect neonatal outcomes: Effect of re-cryopreservation on embryos

Abstract Research Question: Does repeated cryopreservation process affect embryo implantation potential and neonatal outcomes of human embryos? Design: This retrospective cohort study was conducted in the Reproductive Medicine Centre, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology. All assisted reproductive technology (ART) cycles were performed from January 2014 to December 2018. Preferentially matched participants were divided into three groups according to the times of embryo cryopreservation: the fresh group (n=249), the cryopreservation group (n=244) and the re-cryopreservation group (n=216). Embryo implantation rate, live birth rate, miscarriage rate, and neonatal complication rate were compared among these three groups. Results: The embryo implantation rate, clinical pregnancy rate and live birth rate in the re-cryopreservation group were significantly lower, and there was also a slight increase in the miscarriage rate. Logistic regression analysis indicated that embryos with repeated cryopreservation and lower trophectoderm scores were at higher risk of embryo implantation failure in single embryo transfer cycles (OR=1.79 and 1.56 respectively). No significant differences were observed in gender, gestational age, birthweight, neonatal abnormality, and neonatal complications among the groups. Conclusions: Our findings demonstrated the adverse effect of repeated cryopreservation on embryo implantation potential. The study offers embryologists and reproductive clinicians a warning of detrimental role of repeated cryopreservation. If not necessary, it is strongly recommended to avoid repeated practice of vitrification/warming on embryos.