Double vitrification of embryos adversely affects clinical outcomes.

Objective: To evaluate the impact of double embryo vitrification on clinical outcomes.

Methods: This retrospective cohort study included data from January 2013 to March 2021. The study group included women aged 33.3±5.7 years with double-vitrified embryos (n=381), while the control group included women aged 32.1±6.7 years with embryos vitrified once (n=780), all transferred at the blastocyst stage. The primary endpoint was live birth rate (LBR), and secondary endpoints included percent positive βHCG test, clinical/ongoing pregnancy rates, miscarriage/biochemical pregnancy rates and birthweight.

Results: LBR was significantly lower in double-vitrified embryos (30.2%) than in embryos vitrified once (45.6%, p<.05). Similarly, double-vitrified embryos were associated with significantly lower positive βHCG tests (46% vs. 63.3%, p<.05) and 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 embryos: 2950g vs. embryos vitrified once: 2837g, 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 tests (49%) and clinical pregnancy (38%) rates, compared to embryos re-vitrified on the same day of 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).

Conclusions: Double vitrification of embryos adversely affects clinical outcomes. However, it represents a valuable option concerning embryo wastage, with acceptable success rates.