The Impact of Embryo Storage Time on Pregnancy and Perinatal Outcomes and the Time Limit of Vitrification: A Retrospective Cohort Study

Abstract

BackgroundThe technique of embryo cryopreservation has been increasingly applied in clinical settings. However, there has been a concern about the safety and efficacy of long-term freezing of embryos. Therefore, the aim of this study was to evaluate whether storage time of vitrification had any effects on pregnancy as well as perinatal outcomes, further, to explore the appropriate time limit of vitrification.MethodsThe study included women who underwent at least one frozen-thawed cycle with single embryo transfer between January 1st, 2016 and September 30th, 2019. Patients were assigned into 3 groups according to the storage time (<3 months, 3-12 months and >12 months) to evaluate the impact of embryo storage time on pregnancy and perinatal outcomes. To further investigate the time limit of vitrification, propensity score matching was used to compare the primary outcomes of patients with storage time of 1-3 years, 3-5 years, and >5 years to those stored for ≤1 year.ResultsA total of 9806 frozen-thawed embryo transfer cycles were included in our study. After adjustment for confounding variables, no significant differences were found in pregnancy outcomes among groups. However, postponement of transfer increased the risks of large for gestational age and placenta previa. In addition, after propensity score matching, 171 cycles with storage time >5 years were matched with those ≤1 year, both the clinical pregnancy rate and live birth rate decreased significantly when the storage time exceeded 5 years.ConclusionsThe duration of vitrification did not significantly affect the pregnancy outcomes within 5 years period. However, the clinical pregnancy rate and live birth rate both decreased significantly when the duration of vitrification exceeded 5 years. It is worth noting that the conclusion was drawn from a small sample study after propensity score matching and should be treated with caution. In addition, the cycles were from different time periods, which could have an impact on the results.

Effect of exposed-to-air frequency of cryopreserved embryo on clinical outcomes of vitrified-warmed embryo transfer cycles: a retrospective analysis of 9,200 vitrified-warmed transfer cycles

“…Wirleitner et al demonstrated that the cryopreservation storage time has no effect on blastocyst survival and pregnancy outcomes when these blastocysts are stored in the LN 2 tank for up to 6 years [ 11 ]. In contrast, Cui et al showed that the live birth and clinical pregnancy rates decreased significantly when the storage time exceeded 5 years [ 24 ]; however, the sample size of these three studies was small. Recently, two large retrospective analyses showed that the prolonged storage time was negatively associated with pregnancy and live birth [ 14 , 15 ].…”

Can Cryopreservation in Assisted Reproductive Technology (ART) Induce Epigenetic Changes to Gametes and Embryos?

“…Therefore, a decrease in DMSO-induced ATP might cause downstream effects that may disrupt cellular function, fetal development, and implantation potential [ 72 , 73 , 74 , 75 ]. Finally, over the past few years, several reports have shown the detrimental effects of cryopreservation programs on the epigenetic makeup of the embryo, protein expression, and DNA integrity [ 76 , 77 , 78 , 79 , 80 ], as well as alteration of such genes involved in critical biological processes [ 79 , 80 , 81 ], inducing an increase in free radical production and apoptosis [ 81 , 82 , 83 , 84 , 85 ].…”

Risk of genetic and epigenetic alteration in children conceived following ART: Is it time to return to nature whenever possible?

“…These cryoprotectants might affect embryo metabolism, such as protein expression, DNA integrity, and cytoskeletal and nuclear structures 87–90 . A few studies have suggested that CPAs might be linked to epigenetic aberration in oocytes and embryos, and these alterations could be transmitted to future generations 91,92 . Thus, since cryopreservation has become widely used in ART and other fields such as regenerative and transplantation medicine, it is critical to examine potentially genomic and epigenetic changes associated with the current technique.…”

“…[87][88][89][90] A few studies have suggested that CPAs might be linked to epigenetic aberration in oocytes and embryos, and these alterations could be transmitted to future generations. 91,92 Thus, since cryopreservation has become widely used in ART and other fields such as regenerative and transplantation medicine, it is critical to examine potentially genomic and epigenetic changes associated with the current technique. Further epidemiological studies performed on a large scale are necessary to evaluate the implications of the cryopreservation process and the use of CPAs on the health and well-being of the offspring not only at the time of delivery but also during later adult life.…”