Clinical utilization and outcomes over eight consecutive years following oocyte cryopreservation

To compare embryologic and clinical outcomes following oocyte cryopreservation (OC) and immediate fertilization for embryo cryopreservation (EC) in non-infertile patients.

Retrospective cohort study SUBJECTS: Patients treated at a single fertility center from 2016 to 2023.

OC MAIN OUTCOME MEASURES: Blastocyst development was compared between women undergoing OC and non-infertile women undergoing immediate fertilization for EC between 18 and 42 years of age. ICSI, PGT-A, and eSET were used in all cycles.

Outcomes from 3697 thawed MII oocytes obtained from 239 OC patients were compared to 28,959 fresh MII oocytes obtained from 2031 patients undergoing immediate fertilization for EC. Average thaw MII survival rate was 92% and high across age groups. Post-thaw oocytes demonstrate lower fertilization rate compared to fresh oocytes (85% v 90%, p < 0.05). As oocyte age increased, the mean number of MII used per blastocyst increased to a greater extent among thawed compared to fresh oocytes (2.9 v 2.2 MII age 18-34, 3.3 v 2.5 MII age 34-37, 3.9 v 2.9 MII age 38-40, 7.5 v 3.9 MII age 41-42, p < 0.05). Among patients achieving transfer of a euploid blastocyst, clinical pregnancy rate and live birth rate per transfer were similar using thawed and fresh oocytes (p = 0.82 and p = 0.79, respectively).

Blastocyst conversion is lower from thawed oocytes compared to fresh oocytes. Differences in blastocyst development between thawed and frozen oocytes increase with advancing oocyte age, suggesting that older oocytes may be less efficient in their conversion to blastocysts after vitrification and warming.