P-248 Egg vitrification related to female age: survival and laboratory outcome of 1233 vitrified-thawed oocytes in non-medical autologous use
Authors: Cura Ruiz J , Gonzalez Trigo C , Gonzalez Marti B , Entezami F 
Published: July 2024

Abstract

Study question
Is the female age at retrieval a determinant factor for the viability and potential of the thawed eggs?

Summary answer
In patients over 40, thawed oocytes display more abnormal fertilization, develop less in extended culture and yield less top quality blastocyst.

What is known already
Oocyte cryopreservation is a well-established procedure especially since the advent of the vitrification technique. The successful outcomes achieved with vitrification encourage its application in fertility preservation (FP) for medical and non-medical reasons. Besides, the age-related decline in women’s fertility and the oocyte quality negatively affect the outcome of assisted reproduction. Some studies have reported that age at oocyte retrieval strongly influences reproductive prognosis after FP.
However, the appropriate age for non-medical FP is still debated. Although oocyte freezing at a younger age is recommended, there should be a balance between a favourable outcome and the cost-effectiveness of the strategy.

Study design, size, duration
Retrospective study on 166 patients with frozen-thawed oocytes who underwent ICSI during 2021-2023 in a single hospital.
Oocyte vitrification had different purposes: banking for poor responders, to limit the number of embryos, and to solve unexpected situations where partner’s semen sample was unavailable.
Patients were divided into three groups according to their age at retrieval (Group A ≤ 37 n = 77, Group B 37-40 n = 44, Group C ≥ 40 n = 45). Post-warming survival, fertilization, and embryological data were studied.

Participants/materials, setting, methods
1233 oocytes were thawed. The intact oocytes were microinjected 1-2 hours after warming. Embryos were cultured in Sage 1-StepTM to blastocyst stage, and rated on daily basis. Embryo transfer was performed on day 3 or day 5 and remaining blastocysts were frozen on Day 5 or Day 6. Post warming survival, lysis after ICSI, fertilization, embryo development, blastulation rate (BR) and top blastulation rate (TBR), and morphokinetic features were studied in the 3 groups.

Main results and the role of chance
84.6% of the 1233 oocytes (vitrified in a high-security closed system) survived the warming process. 1043 eggs were injected and the post-ICSI lysis rate was 11.2%. No significant differences were seen in thawing survival rate in groups A, B and C (85.6% vs. 83.5% vs. 83.8%, p=0.635) nor in the post-ICSI lysis rate (13.1% vs. 7.4% vs. 11.2%, p=0.072). 2PN fertilization rate was similar between the groups (67.8% vs. 61.3% vs. 67.7%, p=0.178) as well as the total number of embryos (303 vs 146 vs 188 p=0.605). However, triploid fertilization rate (3PN) statistically grew with age (2.8% vs. 5.8% vs. 6.5%, p=0.034). Significant differences were also reported in the global abnormal fertilisation rate (1PN+3PN) (6.4% vs 10.3% vs. 13.3%, p= 0.005). BR and TBR were statistically lower after the age of 40 (BR: 61.5% vs. 62.7% vs 40% p&lt;0.001, TBR: 43.3% vs. 47.9% vs. 24.3% p&lt;0.001).
Morphokinetic features in the 3 groups were studied (abnormal cleavage pattern, tSB and tB).
Overall results were similar between group A and group B but oocyte potential decreases drastically from the age of 40.

Limitations, reasons for caution
The major limitation of the study is its retrospective nature and the relative small size of each group. As most of patients were transferred during 2023, the pregnancies have not delivered yet so the live birth rate is not mentioned.

Wider implications of the findings
Studies have reported the impact of age at oocyte retrieval in case of medical FP in cancer and endometriosis. Here we report a negative effect on outcome after the age of 40 in non-medical FP. Patients should be informed that FP is not a certification of a successful outcome.

Trial registration number
not applicable