P–209 Artificial collapse of human expanded blastocysts protects the quality of embryos during vitrification/warming procedure

Study question Does artificial collapse of human blastocysts before vitrification affect the post warming quality of embryos and/or the reproductive outcome? Summary answer This study suggests that artificial collapse with laser pulse before vitrification significantly benefits blastocyst quality post-warming without improving reproductive outcome. What is known already The efficiency of vitrification of blastocysts can be influenced by various factors, such as the stage of the expansion and the quality of the embryos. Expanded blastocysts seem to be more sensitive and prone to cryo-injury during vitrification because of the large amount of blastocoelic fluid which may cause insufficient dehydration. Artificial collapse (AC) with micro-needles or with laser pulse can improve the vitrification procedure and protect the expanded blastocysts from cryoinjuries by reducing the fluid of the blastocoel. Study design, size, duration This prospective randomized study was performed at Embryolab Fertility Clinic, in Thessaloniki, Greece between July 2020 and November 2020 and included 94 ICSI treatments with no fresh embryo transfer. Patients with more than 4 blastocysts were randomized and allocated to the study (AC) group or control group. Randomization list was created by a computer-based program. The embryos were vitrified at the blastocyst stage and the best 1–2 embryos were transferred in a subsequent cycle. Participants/materials, setting, methods Patients were divided in two groups: AC group (n = 46) where 1 or 2 best expanded blastocysts were artificially collapsed by a laser pulse before vitrification and control group (n = 48) where the corresponding best expanded embryos remained untreated before vitrification. The embryos were graded according to Gardner’s criteria and vitrified using open system. Quality of embryos, pregnancy rate and clinical pregnancy rate from the first warming cycle were the parameters that were analyzed using z-test. Main results and the role of chance The analyzed embryos were in total 171, 85 in the AC group and 86 in the control group. The day 5 embryos in each group were 6.89 (±3.41) and 6.50 (±3.38) and the number of embryos per embryo transfer was 1.85 (±0.36) and 1.79 (±0.41) respectively. Cryoinjury was determined as the presence of degenerated cell in ICM or TE. In the AC group cryo-injury was significantly lower than in the control group [31.11% with at least 1 embryo per embryo transfer and 52.08% respectively (p = 0.0356), 6.67% with cryo-injury in both embryos and 14.58% respectively (p < 0.0001), 8.89% with cryo-injury in ICM and 10.42% respectively (p < 0.0001), 15.56% with cryo-injury in trophectoderm and 27.08% respectively (p < 0.0001), and 6.67% with cryo-injury in both ICM and trophectoderm and 12.50% respectively (p < 0.0001)]. Pregnancy rate (positive b-hcg) was not significantly different between the two groups (62.22% in AC group and 76.09% in control group, p = 0.1479), nor was the clinical pregnancy rate (52.38% and 60.87% in AC and control group respectively, p = 0.4208). Limitations, reasons for caution The number of cases included in this study was limited and the live birth rate was not yet available. More prospective randomized studies are needed in order to validate the benefit of artificial collapse before the vitrification procedure. Wider implications of the findings: Laser artificial Collapse does not compromise expanded blastocyst quality, on the contrary it seems to reduce the amount of cryoinjury observed post warming. Whether it can improve the reproductive outcome, remains to be examined in larger scale studies. Trial registration number Not applicable