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.
Highlights
Embryo cryopreservation, an important derivative of Assisted Reproductive Technology (ART), refers to the technique of keeping embryos in an ultra-low temperature environment for preservation through a series of protective measures, freezing procedures and thawing for transfer when needed [1]
frozenthawed embryo transfer (FET) has the advantages of decreasing the risk of ovarian hyperstimulation syndrome (OHSS) [3, 4] and avoiding the negative effect to endometrium receptivity [5, 6], embryo implantation and placentation [7,8,9] of controlled ovarian hyperstimulation (COH)
The patients were grouped according to storage time
Summary
An important derivative of Assisted Reproductive Technology (ART), refers to the technique of keeping embryos in an ultra-low temperature environment (liquid nitrogen, -196°C) for preservation through a series of protective measures, freezing procedures and thawing for transfer when needed [1]. The application of such technique has widened significantly since the first live birth after a frozenthawed embryo transfer (FET) in 1983 [2]. Embryo cryopreservation mainly includes two techniques, programmed freezing and vitrification Compared with the former, vitrification yields higher survival rate and better clinical outcomes [10]. 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
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