P-118 The critical novel quality control parameter for successful oocyte vitrification: Maintaining solution temperature

Abstract

Study question Does the working solution temperature of vitrification solutions affect oocyte survival and subsequent embryo development to the blastocyst stage? Summary answer Maintaining a working vitrification solution temperature rather than relying on ambient conditions, significantly improves oocyte vitrification efficiency and pre-implantation embryo development parameters. What is known already Vitrification is a widely used method for oocyte cryopreservation, requiring a precise balance of cryoprotectant concentration, temperature, and exposure time. Temperature control is critical, as the meiotic spindle in oocytes is highly sensitive to suboptimal conditions. Vitrification working solution temperature can be affected by multiple parameters such as dish type and volume, prolonged exposure, and airflow all contributing to heat loss. While room temperature is commonly emphasised during vitrification, the impact of the vitrification solution temperature on oocyte survival and embryo development remains underexplored. Study design, size, duration The study included donor oocyte cycles at single private IVF Center, Cyprus (March–December 2024). A total of 157 mature metaphase II (MII) oocytes donated for research were divided into two experimental groups based on temperature conditions consisting of the warm temperature group (n = 70) and the cold temperature group (n = 87). The following outcomes were analysed: oocyte survival and preimplantation embryo development parameters. Statistical analysis included Z-test and t-test for proportion and means comparisons respectively. Participants/materials, setting, methods The study was conducted in a controlled laboratory environment. Cold temperature conditions were maintained with an average room temperature of 22.85±0.84 °C and vitrification solution temperatures at 19.65±0.84 °C. Warm temperature conditions were maintained at an average room temperature of 24.56±0.89 °C, with vitrification solution temperatures at 24 °C. Solution and Room temperatures were recorded using the UNI-T UT322 thermometer, validated with an NIST-traceable mercury-calibrated thermometer. Main results and the role of chance The donor characteristics, including age, BMI, stimulation protocols, and retrieved oocytes, showed no significant differences between groups (p > 0.05). Oocyte survival was significantly higher in the warm group (70/70,100%, 95% CI [1, 1]) compared to the cold group (80/87 (92%), 95% CI [0.8624, 0.9767]; p = 0.0155). Fertilisation rates were comparable between groups (cold:70/80,87.5%, 95% CI [0.8025, 0.9475]; warm: 59/70,84.3%,95% CI [0.7576, 0.9281]; p = 0.575).The cold group showed significantly higher developmental arrest rates at multiple stages: pronuclear (10/70,14.3%, 95% CI [0.0609, 0.2248] vs 0/59,0%, 95% CI [0, 0]; p = 0.0025), zygote (20/70,28.6%, 95% CI [0.1799, 0.3915] vs 0/59,0%, 95% CI [0, 0]; p < 0.001),and cleavage (35/70,50%, 95% CI [0.3829, 0.6171] vs 0/59,0%, 95% CI [0, 0]; p < 0.001). The blastulation rate was significantly higher in the warm group (49/59,83.05%, 95% CI [0.7348, 0.9262]) compared to the cold group (5/70,7.1%, 95% CI [0.0111, 0.1318];p < 0.001). Limitations, reasons for caution Small study sample size and oocyte origin from healthy and fertile young donors limits generalisability for infertile patients. Wider implications of the findings Focusing on the precise temperature of vitrification solutions, rather than room temperature, can enhance oocyte survival and developmental outcomes. This approach improves consistency in oocyte vitrification and offers actionable insights for optimising assisted reproductive technologies, enabling standardised and reproducible results across laboratories and diverse environmental conditions. Trial registration number No