P-096 Shall we achieve full blastocyst collapse after laser-assisted shrinkage prior to vitrification? Retrospective analysis of cryo-survival and clinical outcomes of 995 warmed embryos
V Casciani, G C Cermisoni, M Taggi, F Innocenti, D M Soscia, G Saturno, V Morgante, S Alfano, L Papini, F Sanges, B Iussig, A Vaiarelli, R Maggiulli, D Cimadomo, L RienziAbstract
Study question
Does blastocysts’ degree of collapse achieved through laser-assisted shrinkage (LAS) before vitrification impact live birth rate (LBR) per single embryo transfer (SET) in non-PGT cycles?
Summary answer
Full collapse after LAS is not associated with higher blastocyst cryo-survival or better clinical outcomes in non-PGT cycles.
What is known already
Blastocysts contain significant amount of fluid in their blastocoel cavity which may impair vitrification outcomes. Prior to this procedure, LAS has been suggested to trigger blastocoel cavity emptying, thereby enhancing cryoprotectant diffusion, and improving vitrification safety. A minimal laser pulse, targeting the junction between trophectoderm cells, induces collapse, optimizing vitrification and warming results. Previous studies showed that this approach may improve cryo-survival and clinical outcomes per SET. While LAS is widely used for its safety and efficacy, the impact of partial pre-vitrification shrinkage remains unclear, especially in non-PGT cycles where this procedure is not standard practice.
Study design, size, duration
Observational retrospective cohort study including 995 warmed blastocysts and 992 vitrified-warmed SETs from 637 couples conducted after LAS at a private IVF center (years:2019-2022). We compared cryo-survival rate, positive pregnancy test (PPT) per SET, biochemical pregnancy loss (BPL) per PPT, miscarriage per clinical pregnancy, LBR per SET (primary outcome), and twinning rate per delivery, among partially- versus fully-collapsed blastocysts before vitrification.
Participants/materials, setting, methods
A laser pulse was applied at junctions between two trophectoderm cells to induce controlled micro-disruption and shrinkage. Before proceeding with vitrification after 1 minute from LAS, the blastocysts’ status was qualitatively assessed as either partially- (N = 407) or fully-collapsed (N = 588). Generalized estimating equations (GEE) were adopted to adjust for repeated ETs from the same patient in logistic regression analyses.
Main results and the role of chance
Possible confounders were assessed, including age at oocyte retrieval and ET, donor/own eggs, BMI at ET, blastocyst expansion at ET, inner cell mass and trophectoderm quality (Gardner’s grading), culture day (5–7), endometrial preparation (modified-natural/artificial cycle), consecutive vitrified-warmed ET of the working day, and hours between warming and ET automatically-annotated with electronic witnessing system (both continuous and categorized as before or after the median timing of 3 hours). No differences in potential confounders were observed between the two study groups. Results indicate a very high and comparable cryo-survival rate (N = 405/407, 99.5% among partially-collapsed versus N = 587/588,99.8% among fully-collapsed; p = 0.571) in both groups, confirming LAS safety. Additionally, partial-collapse showed no association with all outcomes, including the LBR per SET even when adjusting for confounders (N = 125/405, 30.9% among partially-collapsed versus N=N=174/587,29.6% among fully-collapsed; OR = 0.97, 95%CI:0.73-1.29, p = 0.829). The results were confirmed also in a sub-analysis including only first SETs conducted by each couple. Neither the consecutive ET of the working day, nor the hours between warming and ET were associated with the LBR. Only a decreasing trend for ETs conducted beyond 3 hours was shown, yet not significant (N = 188/591,31.8% before 3hours and N = 111/401,27.7% after 3hours, p = 0.093).
Limitations, reasons for caution
Single-center retrospective study. The information is relevant only for laser-assisted protocols to induce blastocyst’s shrinkage. Morphometric data (e.g., area in µm2) were not annotated, and will be the object of future investigations.
Wider implications of the findings
LAS is confirmed beneficial to maximize post-warming cryo-survival. After this procedure in non-PGT cycles, it might be unnecessary achieving full-collapse before starting the vitrification process, as no impact on clinical outcomes has been reported. The time between warming and ETs seems not to impact the LBR, especially if < 3hours.
Trial registration number
No