P–162 Laser-assisted collapse of blastocysts prior to vitrification improves clinical outcomes

Study question What is the effect of artificial laser-assisted collapse before vitrification on pregnancy and implantation rates after transfer of vitrified-warmed blastocysts? Summary answer The artificial shrinkage by laser-induced collapse before vitrification significantly increased the implantation and clinical pregnancy rates after single thawed embryo transfer. What is known already Freeze all, cycle segmentation and, in general, single embryo transfer (SET) strategies (for example trophectoderm biopsy-based aneuploidy testing) have targeted blastocysts vitrification as the best option for reproductive practice worldwide. Artificial shrinkage seems to be a pre-vitrification parameter associated with an increased embryo survival after warming and implantation rate. However, the available medical evidence shows controversial results with only a limited number of prospective studies assessing the subject. Study design, size, duration This prospective cohort study evaluated 394 women who underwent a frozen blastocyst transfer at Instituto Bernabeu between July and December 2020. All patients were prepared with substitutive cycle and received single blastocyst embryo transfers. Participants/materials, setting, methods Before embryo vitrification on day 5 of development, some expanded and/or early hatching blastocysts (A/B ASEBIR categories) were artificial laser-assisted collapsed. (n = 83, study group). 311 embryos of the same quality and day of development were not collapsed (control group). We compared the embryo survival rate, clinical, implantation and miscarriage rates between groups. The statistical analysis was performed using SPSS (version 20.0). Main results and the role of chance The two groups were comparable in terms of maternal age (39.79 ± 3.83, control group; 40.21 ± 4.45, study group; p = 0.341). Embryo survival rate resulted in 100% in both groups. Regarding clinical outcomes, collapsed blastocysts significantly increased the positive pregnancy test and the clinical pregnancy and implantation rate compared to the control group, respectively (positive test: 69,9% vs 43,4%, p = 0.000018, odds ratio (OR)= 3.02 [95% CI 1.80–5.08]; clinical pregnancy and implantation: 56,6% vs 35,4%, p = 0.000041, OR = 2.39 [95% CI 1.46–3.90]). The miscarriage rate was not affected by the blastocyst collapse effect (23,6% in the control group vs 27,6% in the study group, p = 0.593, OR = 1.23 [95% CI 0.57–2.68]). Limitations, reasons for caution This is a non-randomized controlled study. Additional RCTs are warranted to corroborate our findings. Wider implications of the findings: Considering the large number of blastocyst vitrification cycles that are carried out worldwide, artificial laser-assisted collapse before vitrification has the potential to increase the clinical results in benefit of many patients. Trial registration number Not applicable