Effects of Vitrified Cryopreservation Duration on the IVF and Neonatal Outcomes

Abstract Objective: To evaluate the impact of cryopreservation storage duration on embryo viability, implantation competence, pregnancy outcome and neonatal outcomes.Design: Retrospective study.Setting: Center for Reproductive Medicine，The Third Affiliated Hospital of Guangzhou Medical University.Patient(s): In vitro fertilization patients who had vitrified cryopreserved embryos and following the first frozen embryo transfer cycles from January 2004 to August 2019. A total of 31143 patients met the inclusion criteria and were grouped according to the storage time (20926 patients in Group 1 with storage time <3 months, 6472 patients in Group 2 with storage time between 3 and 6 months, 2237 patients in Group 3 with storage time between 6 and 12 months and 746 in Group 4 with storage time between 12 and 24 months, 762 patients in Group 5 with storage time >24 months).Intervention(s): None.Main Outcome Measure(s): In the total FET cycles, the embryo survival rate was decreased significantly with the increase of cryopreservation time, and the highest rate was 98. 63 % in the 1-3 months group, and the lowest was 71.13% in the >=731 days group (P <0. 01). The HCG positive rate (57.85%) and clinical pregnancy rate (55. 26%) in the 1-3 months group were the highest (P=731 group had the lowest sex ratio of 0.96. There were no significant differences in neonatal birth weight, neonatal height and congenital anomalies among the groups (P>0. 05).Result(s): Length of storage time had a significant effect on post-thaw survival and outcomes for IVF cycles. Conclusion(s): With the prolongation of cryopreservation time, the embryonic survival rate and pregnancy rate were decreased significantly. Short-term cryopreservation (<=3 months) can obtain higher clinical pregnancy rate. Therefore, although long-term hryopreservation of the embryo has no effect on the health of the new baby, but hryopreserved embryos should be recovery as soon as possible if condition allows.