Received July 19, 2023
Accepted January 21, 2024

Objective: To evaluate the impact of double embryo vitrification on clinical outcomes. Methods: Retrospective cohort study, including data from January 2013 to March 2021. Study group included women of mean age 33.3(SD: +5.7)with embryos vitrified twice(n=381), while control group included women of mean age 32.1(SD: +6.7) with embryos vitrified once(n=780), all transferred at the blastocyst stage. The primary outcome was live birth rate(LBR),while secondary outcome measures included positive βHCG rate, clinical/ongoing pregnancy rates, miscarriage/biochemical pregnancy rates and birthweight. Results: LBR of double vitrified embryos(30.2%) was significantly lower than LBR of embryos vitrified once (45.6%, p<.05). Similarly, double vitrified embryos demonstrated significantly lower positive βHCG rate(46% vs 63.3%, p<.05), clinical(34.9% vs 52.2%, p<.05)and ongoing pregnancy(31.3% vs 47.3%, p<.05) rates compared to embryos vitrified once. However, biochemical pregnancy(double vitrified:24.1% vs vitrified once:17.9%, p>.05)and miscarriage rates(double vitrified:10.2% vs vitrified once:9.4%, p>.05),as well as mean birthweight(double vitrified:2950gr vs vitrified once:2837gr, p>.05)did not differ significantly between two groups. On a secondary comparison, amongst double vitrified embryos, the subgroup that was cultured for more than 24 hours between warming and second vitrification achieved significantly higher positive βHCG(49%)and clinical pregnancy(38%)rates, compared to embryos re-vitrified on the same day of their warming(31.8% and 20.5%, respectively, p<.05). Nevertheless, LBR did not differ significantly amongst these study-group embryos(embryos that remained in culture for more than 24 hours: 32.2% vs embryos that were re-vitrified on warming day: 20,5%, p>.05). Conclusion: Double vitrification of embryos adversely affects clinical outcomes. However, it represents a valuable option concerning embryo wastage, with acceptable success rates.