Clinical utilization and outcomes over eight consecutive years following oocyte cryopreservation.
Level 3 - non-randomized controlled study
Retrospective comparative cohort study
PubMed 39633145 · doi:10.1007/s10815-024-03334-z
What was done
This retrospective cohort study compared embryologic and clinical outcomes between oocyte cryopreservation (OC) and immediate fertilization for embryo cryopreservation (EC) in non-infertile women aged 18 to 42 treated at a single fertility center between 2016 and 2023. All cycles used intracytoplasmic sperm injection (ICSI), preimplantation genetic testing for aneuploidy (PGT-A), and elective single-embryo transfer (eSET). Outcomes were compared between 3,697 thawed metaphase II (MII) oocytes from 239 OC patients and 28,959 fresh MII oocytes from 2,031 EC patients.
What was found
Thawed MII oocyte survival averaged 92% across age groups. Thawed oocytes had a significantly lower fertilization rate than fresh oocytes (85% vs 90%, p < 0.05). The mean number of MII oocytes required per blastocyst was significantly higher for thawed versus fresh oocytes across all age brackets (p < 0.05): 2.9 vs 2.2 (ages 18–34), 3.3 vs 2.5 (ages 34–37), 3.9 vs 2.9 (ages 38–40), and 7.5 vs 3.9 (ages 41–42). Among patients who reached euploid embryo transfer, clinical pregnancy rates (p = 0.82) and live birth rates (p = 0.79) per transfer were similar (exact percentages not reported in abstract).
Why it matters
These findings provide age-stratified benchmarks for oocyte-to-blastocyst efficiency, helping clinicians provide realistic counseling to women freezing eggs regarding how many oocytes they may need depending on age.
Limits
The study is retrospective and conducted at a single fertility clinic, which may limit generalizability across different laboratory protocols. The OC cohort was substantially smaller than the EC cohort (239 vs 2,031 patients). The abstract does not provide exact percentages for clinical pregnancy or live birth rates, nor long-term neonatal outcomes.
Cited by
- supports In standard IVF culture, approximately 90% of frozen eggs survive thawing, 75% fertilize, 50% reach the blastocyst stage, and a genetically normal (euploid) embryo has roughly a 65% chance of resulting in a live birth.