Duration of cryostorage is not associated with rates of thaw survival, fertilization, blastulation and ploidy, or pregnancy outcomes of vitrified human oocytes

Purpose: This study is to evaluate duration of oocyte cryostorage and association with thaw survival, fertilization, blastulation, ploidy rates, and pregnancy outcomes in patients seeking fertility preservation.

Methods: Retrospective cohort study to evaluate clinical outcomes in patients who underwent fertility preservation from 2011 to 2023 via oocyte vitrification for non-oncologic indications. Primary outcome was thaw survival rate. Secondary outcomes included rates of fertilization, blastulation and embryo ploidy, as well asn pregnancy outcomes. Demographic, controlled ovarian stimulation, and laboratory data were collected for each patient. Analyses were conducted using Kruskal-Wallis, Fisher's exact test, or Chi-squared test, as appropriate. A multivariate logistic regression analysis was utilized, and adjusted odds ratios with 95% confidence intervals were calculated using Group A as the reference group.

Results: A total of 5995 oocytes met inclusion criteria. These were divided into quartiles based on duration of cryostorage. Group A included oocytes in cryostorage for 0-2 years; Group B, 3-5 years; and Group C, 6-11 years. Significant differences were found when comparing thaw survival (p < 0.0001), fertilization (p = 0.0009), and blastulation rates (p = 0.0002) among groups; however, no significant differences were seen after multivariate GEE regression analysis. No significant differences were seen in rates of euploidy (p = 0.70), live birth (p = 0.81), and clinical pregnancy (p = 0.58) among groups. After analyzing years in cryostorage as a continuous variable and controlling for confounders, duration of cryostorage was not related to odds of thaw, fertilization, blastulation, euploid rates, or pregnancy outcomes.

Conclusion: Length of time in cryostorage is not associated with compromised rates of oocyte thaw survival, fertilization, blastulation, ploidy, or pregnancy outcomes.