Long-term storage of vitrified oocytes does not affect pregnancy and live birth rates: analysis of 5362 oocyte donation cycles

Research question: Does long-term storage of vitrified oocytes affect laboratory and reproductive outcomes after intracytoplasmic sperm injection?Design: Retrospective cohort study including 41,783 vitrified-warmed oocytes from 5362 oocyte donation cycles between 2013 and 2021. Five categories of storage time were established to analyse its effect on clinical and reproductive outcomes (<= 1 year [reference group], 1-2 years, 2-3 years, 3-4 years and >4 years).Results: The mean number of warmed oocytes was 8.0 +/- 2.5 oocytes. Oocyte storage time ranged from 3 days to 8.2 years (mean: 0.7 +/- 0.9). Mean oocyte survival (90.2% +/- 14.7% overall) did not significantly decrease with longer storage time after adjusting for confounders (88.9% for time >4 years, P = 0.963). A linear regression model did not show a significant effect of oocyte storage time on fertilization rate (about 70% in all time categories) (P > 0.05). Reproductive outcomes after the first embryo transfer were statistically comparable across storage times (P > 0.05 for all categories). Longer term oocyte storage (>4 years) did not affect the chances of clinical pregnancy (OR 0.700, 95% CI 0.423 to 1.158, P = 0.2214) or live birth (OR 0.716, 95% CI 0.425 to 1.208, P = 0.2670).Conclusions: Oocyte survival, fertilization rate, pregnancy and live birth rates are not affected by the time spent by vitrified oocytes in vapourphase nitrogen tanks.

Automated summary

This retrospective cohort study examined the effects of long-term storage of vitrified oocytes on laboratory and reproductive outcomes. The results showed that the storage time did not significantly impact oocyte survival, fertilization rate, pregnancy, and live birth rates.