JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):47
Poster Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263586

P-35. Blastocyst Formation Rate, Rather Than Oocyte Number, Predicts Cumulative Live Birth in Donor Oocyte Cycles

Carine Lima¹, Danielle Deveza¹, Andressa Gonçalves Mendes¹, Bruna Armond¹, Adriana Ferreira Homem¹, Amanda Oliveira¹, Marcello Pereira Valle¹

¹Origen Rio - Rio de Janeiro - RJ - Brasil

Objective: In vitro fertilisation (IVF) with donor eggs is a widely used treatment for women unable to conceive with their own oocytes. Donor cycles often use vitrified oocytes, but evidence suggests that damage from vitrification and warming may reduce the number suitable for ICSI. This study aimed to assess the impact of the number of thawed and surviving vitrified oocytes on clinical outcomes in donor cycles and to estimate the average number needed to achieve a live birth.
Methods: This retrospective cohort study included 447 ICSI cycles with vitrified donor oocytes, performed between 2012 and 2024. Demographic, laboratory, and clinical data were analysed. Cycles were stratified by the number of thawed oocytes (4–6, 7–9, ≥10) and surviving oocytes (3–4, 5–6, 7–9, ≥10). Groups were compared for clinical outcomes. Multivariable logistic regression was used to assess the independent effects of oocyte number and blastocyst formation rate on cumulative live birth rate (CLBR), adjusting for recipient, donor, and paternal age, as well as sperm concentration.
Results: In the study population, the mean age was 43.1 ± 4.3 years for recipients and 27.1 ± 4.9 years for donors. The mean number of warmed oocytes was 7.6 ± 1.8, with a survival rate of 94.7% and a fertilisation rate of 78.1%. The blastocyst formation rate was 41.5% per warmed oocyte and 43.9% per surviving oocyte. The CLBR among ongoing cycles was 49.5% (355 embryo transfers) and 71.1% among completed cycles (232 embryo transfers). No significant differences were observed among groups with 4–6, 7–9, and ≥10 warmed oocytes in pregnancy rate after the first embryo transfer (50.3%, 49.7%, and 48.6%, respectively; p=0.981), CLBR among ongoing cycles (50.3%, 47.3%, and 57.1%, respectively; p=0.556), or CLBR among completed cycles (64.9%, 76.3%, and 79.2%, respectively; p=0.127). A similar pattern was observed when groups were defined by the number of surviving oocytes, with pregnancy rates of 38.5%, 51.6%, 50.0%, and 43.3% (p=0.702), CLBR among ongoing cycles of 38.5%, 51.6%, 46.8%, and 53.3% (p=0.680), and CLBR among completed cycles of 50.0%, 67.4%, 80.0%, and 78.9% (p=0.1037). In multivariable logistic regression analysis, the blastocyst formation rate per warmed oocyte was positively associated with cumulative pregnancy, independent of the number of surviving oocytes and other potential confounders; each 1.0% increase in blastocyst formation rate corresponded to a 2.0% increase in the odds of pregnancy (OR = 1.020; 95% CI, 1.006–1.034; p=0.002). The number of surviving oocytes was not significantly associated with pregnancy outcome (OR = 0.933; 95% CI, 0.823–1.058; p=0.257). Results for CLBR were consistent, with the blastocyst formation rate again showing a positive association (OR = 1.020; 95% CI, 1.008–1.032; p=0.002), independent of the number of surviving oocytes (OR = 0.904; 95% CI, 0.814–1.005; p=0.088) and other covariates. Based on programme-specific performance estimates, achieving one live birth required an average of 6.8 warmed donor oocytes or 6.3 surviving oocytes post-warming, underscoring the importance of laboratory efficiency in converting oocytes into viable blastocysts as a key determinant of success in donor oocyte programmes.
Conclusions: The absolute number of warmed or surviving oocytes was not directly associated with cumulative live birth rates. Instead, the blastocyst formation rate was the strongest predictor of clinical success, underscoring that the efficiency of the laboratory in oocytes into viable blastocysts outweighs the impact of oocyte count alone. In practical terms, approximately six surviving oocytes are required to achieve a live birth given current programme performance, reinforcing that both oocyte quality and laboratory performance should be prioritised over quantity. Each laboratory should establish its own performance metrics to guide allocation and utilisation strategies in donor oocyte programmes.