Assessing the reproductive potential of late mature cryopreserved oocytes

Are there any differences in the warming, fertilization and embryo development outcomes of late mature cryopreserved oocytes versus immediately mature cryopreserved oocytes?

This retrospective cohort study analysed autologous oocyte cryopreservation cycles with warming from January 2016 to September 2024. Group 1 comprised oocytes that were mature [metaphase II (MII)] at retrieval (assessed within 1 h of retrieval), and Group 2 comprised late mature oocytes, which included day 0 and day 1 late mature oocytes, which reached MII on re-assessment after short term (4-6 h) and next-day (18-28 h) rescue in-vitro maturation, respectively. Comparative statistics and univariate analysis were performed using Wilcoxon rank sum test and chi-squared test. Logistic regression fitted with a generalized estimating equation, adjusted for oocyte age, anti-Müllerian hormone, body mass index, year of oocyte cryopreservation and year of oocyte warming, was performed for warming survival, fertilization, blastulation and ploidy rates.

Among 565 patients (699 cryopreservation and 629 warming cycles), Group 1 included 6899 oocytes that were mature at retrieval and Group 2 included 956 late mature oocytes. The warming survival rate was comparable between the groups (79.4% versus 78.0% for Groups 1 and 2, respectively; P = 0.33). The fertilization rate was significantly higher in Group 1 (75.3%) than Group 2 (59.8%) (adjusted OR 0.52, 95% CI 0.42-0.63; P < 0.001). Group 1 had significantly higher blastulation (37.7% versus 26.1%; P ≤ 0.001) and euploidy (54.5% versus 39.3%; P = 0.0023) rates compared with Group 2, and this was confirmed on adjusted analysis. A subanalysis showed no difference between day 0 and day 1 late mature oocytes.

Late mature cryopreserved oocytes show lower reproductive potential than oocytes that are mature at retrieval. This could be attributed to dysynchronous cytoplasmic and nuclear maturation. Despite suboptimal development, late mature oocytes can create high-quality blastocysts, offering additional opportunities for future family-building.