P-160 The effect of laser assisted hatching (AHΑ) on vitrified-warmed blastocysts post warming on reproductive outcome

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Abstract Study question Does laser assisted hatching (ΑΗΑ) of vitrified-warmed blastocysts post warming improve the pregnancy rates? Summary answer This study suggests that although laser assisted hatching post warming shows a trend towards improving pregnancy rates, the difference is not significant. What is known already It is known that vitrification may alter the zona pellucida’s biochemical properties and possibly cause hatching failure and ultimately implantation failure. One proposed way in order to overcome this drawback, is the implementation of laser assisted hatching. During assisted hatching, multiple laser shots are performed in the perivitelline space creating an opening on the zona pellucida which facilitates the blastocyst’s herniation process. The efficiency of this method in regard to pregnancy outcomes though, remains controversial. Some studies report a significantly positive effect on pregnancy outcomes using laser assisted hatching whereas others report no significant difference. Study design, size, duration This prospective randomized study was performed at Embryolab Fertility Clinic, in Thessaloniki, Greece between January 2020 and October 2020 and included 2439 frozen embryo transfers. Patients with vitrified-warmed embryos were randomized and allocated to the study (ΑHA) group or control (NO AHA) group. Participants/materials, setting, methods Patients were divided in two groups: AΗΑ group (n = 1799) where laser assisted hatching was performed on the day of embryotransfer (Day 3 or Day 5) on the zona of the embryos post warming and control group (n = 640) where the embryos remained untreated after the warming procedure. The 2 groups were further divided in 3 subgroups depending on the women’s’ age (≤35, 36-40, ≥41) and in 2 more subgroups depending on the day of the transfer. Main results and the role of chance Mean pregnancy rate for all embryos’ stages in AHA group was 60.03% whereas in the NO AHA group was 58.28% (p = 0.4385). In the subgroup of ≤ 35-years, pregnancy rates were 70.23% and 66.49% respectively (p = 0.3363). In the 36-40years subgroup, rates were 58.24% and 60.09% respectively (p = 0.6418). And finally, in the ≥41-years subgroup, pregnancy rates were 54.26% and 49.79% respectively (p = 0.2331). In the group where the embryos were on cleavage stage, the overall pregnancy rate for the AHA group was 27.46 and for the NO AHA group was 35.42% (p = 0.2957). In the subgroup of ≤ 35-years, pregnancy rates were 44.44% and 58.33% respectively (p = 0.4231). In the 36-40years subgroup, rates were 33.33% and 42.86% respectively (p = 0.5236). And finally, in the ≥41-years subgroup, pregnancy rates were 18.42% and 18.18% respectively (p = 0.9796). In the group where the embryos were on blastocyst stage, the overall pregnancy rate for the AHA group was 62.82% and for the NO AHA group was 60.14% (p = 0.2486). In the subgroup of ≤ 35-years, pregnancy rates were 71.66% and 67.03% respectively (p = 0.2430). In the 36-40years subgroup, rates were 60.16% and 61.31% respectively (p = 0.7786). And finally, in the ≥41-years subgroup, pregnancy rates were 58.37% and 53.08% respectively (p = 0.1763). Limitations, reasons for caution Clinical pregnancy rates and live birth rates were not available so as to draw a safer conclusion regarding the effectiveness of the method. In contrast to all kind of cases (both homologous and heterologous cycles) having been pooled together, an appropriate subgrouping might would have been the optimal approach. Wider implications of the findings AHA before transfer of vitrified/warmed embryos does not improve pregnancy rates regardless of stage or age. Nevertheless of the trend towards improving pregnancy rates, the difference is not statistically significant. Large scale, well-designed and appropriately subgrouped studies are necessary in order to investigate if this trend can become statistically significant. Trial registration number N/A