Comparative Embryological Outcomes of Vitrified and Fresh Oocytes in Patients with Diminished Ovarian Reserve

Background: The number of oocytes retrieved is a key determinant of in-vitro fertilization (IVF) success, positively associated with fertilization rate, blastocyst formation, and cumulative live birth outcomes. Optimal results are observed in cycles retrieving 16–20 oocytes, with no decline in cumulative live birth rate at higher yields. Objective: This study aimed to compare embryological outcomes between vitrified and fresh oocytes in the same patients with diminished ovarian reserve. Methods: This retrospective study included 114 women with diminished ovarian reserve (DOR) who underwent oocyte accumulation using both vitrified and fresh oocytes between June 2021 and January 2025. A total of 400 vitrified and 291 fresh oocytes were analyzed. The survival rate, fertilization rate, cleavage rate, and day-2 embryo quality were compared. Subgroup analysis was performed according to POSEIDON groups 3 (<35 years) and 4 (≥35 years). Pregnancy outcomes were preliminarily evaluated in 52 patients who underwent frozen embryo transfer using embryos derived from both oocyte types. Results: The mean survival rate was 93.1% ± 14.6%. No significant differences were observed between vitrified and fresh oocytes in fertilization rate (79.7% vs. 86.0%, p = 0.41), cleavage rate (90.8% vs. 93.9%, p = 0.31), or day-2 embryo quality (p > 0.05). Embryological outcomes were comparable in both POSEIDON 3 and 4 groups. In group 4, the proportion of grade 3 embryos was higher in the vitrified oocyte group than in the fresh group (16.0% vs. 9.5%), but this difference was not statistically significant. The overall pregnancy and clinical pregnancy rates were 51.9% and 36.5%, respectively. Conclusion: Oocyte vitrification is a feasible and effective strategy for oocyte accumulation in women with DOR, yielding comparable embryological outcomes to fresh oocytes. This approach may offer a valuable option for improving reproductive outcomes in low-prognosis patients.