P-401 The impact of the recipients’ age in vitrified/warmed oocyte donation (OD) cycles

Study question: Does female age affect reproductive outcomes in a vitrified/ warmed OD program with fresh embryo transfer? Summary answer: Oocyte donation performed below the age of 40 was associated with less favorable reproductive outcomes. What is known already: It is well established that oocyte and embryo aneuploidy are mainly responsible for the age-related decline in female fertility. Previous studies evaluating the effect of maternal age on implantation potential in OD cycles generated controversial results. It remains unclear whether female age affects reproductive outcome independent of embryo quality. Study design, size, duration: This is a retrospective, single tertiary center, cohort study analyzing a vitrified/warmed OD program over a ten-years period (February 2010-February 2020). More specifically, data from 491 unique oocyte recipients were included who performed a fresh embryo transfer after sharing (with at least two recipients) sibling oocytes from the same donor stimulation cycle. For all treatments ICSI was performed without preimplantation genetic testing. Participants/materials, setting, methods: The association between recipient's age and reproductive outcomes was investigated according to three age categories (40 years old). The primary outcome was live birth rate (LBR), while the secondary outcome was biochemical pregnancy rate (BPR). A multivariate regression model was developed adjusting for the following covariates (entered simultaneously): recipient's BMI, recipient's endometrial thickness, age of the oocyte donor, number of mature oocytes used for ICSI, embryo transfer stage and number of embryos transferred. Main results and the role of chance: Mean age of donors was 28.6 years old(±4.1). Mean starting dose was 192.6 IU(±139.9) and duration of stimulation 11.0 days (±1.7). Mean number of collected cumulus oocyte complexes was 25.6(±9.6) and sibling oocytes were assigned to 2, 3 or more recipients in, respectively, 83.1%, 12.4% and 4.5% of cases. Mean age of recipients was 38.6 years old(±5.1), BMI 24.3 kg/m2(±4.1) and endometrial thickness 8.9mm(±2.1). ICSI was performed on a mean number of 6.5 (±2.0) warmed, intact, mature oocytes with a fertilization rate of 68.2% (±22.5). Cleavage-stage embryos were transferred in 91.0% of the recipients, with a double embryo transfer in 42.6%. 81.3% of embryos were scored as top-quality and a mean of 1.4 (±1.4) surplus embryos were available for additional vitrification. Overall BPR was 44.2%, clinical pregnancy rate 39.3% and LBR 31.0%. Categorizing according to recipient's age showed a LBR of 24.3%,26.7% and 37.0% for, respectively, the group 40 years old (p=0.02). The multivariate GEE regression model confirmed the crude data showing that the age was a significant positive predictor of LBR [coefficient (-), 0.01,0.11, for group40 years old, p=0.05] and BPR [coefficient (-),0.008,0.15, for group 40 years old, p=0.006]. Limitations, reasons for caution: Sibling donor oocytes were used, but the retrospective nature of the study remains a reason for caution. Also, the fact that the majority of embryos were transferred at the cleavage stage is a limitation. Wider implications of the findings: The observation that recipients below the age of 40 have lower reproductive success rates following oocyte donation deserves further attention. The need for oocyte donation at younger age might be associated with a less performant uterine/endometrial function due to underlying conditions of genetic and/or endocrine nature.