The effect of recryopreservation on embryo viability and outcomes of in vitro fertilization: a systematic review and meta-analysis

Abstract

Objective: To investigate the impact of recryopreservation on embryo viability and the outcomes of in vitro fertilization (IVF) by comparison with single cryopreservation. There is a lack of consensus and reliable evidence regarding the impact of recryopreservation techniques on human embryos, particularly with respect to embryo viability and IVF outcomes.

Design: Systematic review and meta-analysis.

Setting: Not applicable.

Intervention(s): Various databases such as PubMed, Embase, Cochrane Library, and Scopus were searched until October 10, 2022. All comparative studies comparing embryonic and IVF outcomes between repeated and single cryopreservation of embryos were included. The random-effect and fixed-effect meta-analysis models were used to pool the odds ratio (OR) and corresponding 95% confidence intervals (CIs). A subgroup analysis was performed based on different methods of cryopreservation and different times of embryo cryopreservation or transfer.

Main outcome measure(s): Outcomes referring to embryo surviva l, IVF outcomes (including clinical pregnancy rate, embryo implantation rate, miscarriage rate, and live birth rate), and neonatal outcomes (including low birth weight rate and preterm birth rate) were evaluated.

Result(s): Fourteen studies were eligible for the present meta-analysis, involving 4,525 embryo transfer cycles in total (3,270 cycles with single cryopreservation [control group] and 1,255 with recryopreservation [experimental group]). Decreased embryo survival (OR, 0.51; 95% CI, 0.27-0.96) and clinical pregnancy rates (OR, 0.47; 95% CI, 0.23-0.96) were found in embryos that were recryopreserved by slow freezing. The live birth rate of revitrified embryos was also notably affected (OR, 0.60; 95% CI, 0.38-0.94). Overall, recryopreservation resulted in a decreased live birth rate (OR, 0.67; 95% CI, 0.50-0.90) and an increased miscarriage rate (OR, 1.52; 95% CI, 1.16-1.98) compared with single cryopreservation. No significant difference was found in neonatal outcomes. When embryos were cryopreserved and transferred at the blastocyst stage, both the embryo implantation rate (OR, 0.59; 95% CI, 0.39-0.89) and live birth rate (OR, 0.60; 95% CI, 0.37-0.96) were significantly different between the 2 groups.

Conclusion(s): The present meta-analysis suggested that recryopreservation, compared with single cryopreservation, can lead to impaired embryo viability and a lower rate of IVF success, with no affected neonatal outcomes. Clinicians and embryologists should retain a cautious attitude toward recryopreservation strategies.

Registration number: CRD42022359456.

Keywords: Recryopreservation; embryo cryopreservation; embryo viability; frozen embryo transfer; in vitro fertilization.