P–251 To collapse or not to collapse blastocysts before vitrification? A matched case-control study on single vitrified-warmed blastocyst transfers

Abstract Study question Does laser-induced artificial blastocoel collapse result in better blastocyst cryopreservation survival and higher live birth rate (LBR) in comparison with intact counterparts? Summary answer Compared to vitrification of intact blastocysts, collapsed blastocysts resulted in higher survival and for 5% higher LBR. Neonatal outcomes were comparable in both groups. What is known already Blastocysts have long been considered a stage that is suboptimal for freezing-thawing procedures due to their high fluid content and different cell types. The development of a modified vitrification technique has enabled blastocysts to better survive cryopreservation compared to a slow freezing procedure. Many studies on the optimization of cryopreservation of blastocysts have mentioned the need for artificial collapsing of the blastocoel prior to cryopreservation, thereby reducing the risk of intracellular ice-crystals formation. However, the effectiveness of artificial collapsing on blastocyst survival rate, single vitrified-warmed blastocyst transfer (SVBT) outcome and on safety of such intervention remains to be confirmed. Study design, size, duration A retrospective matched case-control study of transfers of single blastocysts being artificially collapsed (case) or intact (control) before vitrification. A sample size of 306 cycles in both arms was needed to achieve 80% power to detect a difference between the groups of 10% with P