Is There Any Benefit in Artificial Collapse of Human Blastocysts Prior to Vitrification?

Today, vitrification of human blastocysts provides an excellent outcome although a big water filled cavity called the blastocoele needs to be dehydrated prior to the cooling steps of vitrification. The replacement of water by the cryoprotectant seems to be the supported by artificially collapsing of the blastocoel. Therefore we started to apply artificial collapsing on human blastocysts using a laser pulse prior to vitrification, and then compared outcome data with frozen embryo transfers (FET), where no artificial collapse was applied. Retrospective analysis. A total of 1395 FET (average age 35.1±5.0) including day 5/6 blastocysts without artificial collapsing (group A) were performed. The study group with artificial collapsing (group B) consisted of 143 FET (day 5/6) with an average patient age of 35.3±4.9. Prior to vitrification, the junction between two trophectoderm cells in the blastocyst was located and one laser shot at 100% power with a 500ms pulse (Hamilton Thorne) was released. The High Security Vitrification Kit (CryoBioSystem, France) was used as a closed carrier, with a mixture of 15% Ethylene Glycol/Dimethyl Sulfoxide (v/v)+0.5M sucrose. Statistical significance was evaluated by Chi-Square. No significant difference in the survival between group A and B (98.5% vs. 98.5%) as well as in the mean number of embryos transferred was observed (1.8 vs. 1.8). However, group B had a significant higher clinical pregnancy and implantation rate than group A (63.6% vs. 45.0%; P<.001) and 49.0% vs. 33.0%; P<.001, respectively. The overall ongoing pregnancy in group A was significant lower than in group B (38.5% vs. 58.7%; P<.001). This study demonstrates that artificially collapsing of day 5/6 blastocysts prior to the steps of vitrification is beneficial for all outcome parameters including clinical and ongoing pregnancy rate as well as implantation rate. Using a laser, the procedure is fast, simple and precise, with the benefit of improvement in outcome.