Retrospective clinical analysis of two artificial shrinkage methods applied prior to blastocyst vitrification on the outcome of frozen embryo transfer.

PURPOSE: Vitrification significantly improves the rates of blastocyst survival and clinical pregnancy following frozen embryo transfer (FET). However, ice crystal formation during the freezing process reduces the blastocyst survival rate. Artificial shrinkage (AS) prior to blastocyst vitrification decreases the formation of ice crystals, increasing the blastocyst survival rate. The aim of this study was to identify an efficient AS method to improve blastocyst survival rates following vitrification.
METHOD: Use of the 29-gauge needle AS and Laser pulse AS methods prior to vitrification was compared in terms of the impacts on the rates of blastocyst survival in FET cycles, blastocyst hatching, clinical pregnancy after transfer, embryo implantation, abortion, gestational duration and birth weight. RESULT: In total, 438 blastocysts in 219 cycles were thawed, resulting in survival of 407 (92.9 %). Of these, 213 cycles were transferred, resulting in 129 clinical pregnancies (60.6 %) and 140 successful births. There were no differences between the two methods in the rates of blastocyst survival, clinical pregnancy, embryo implantation and abortion. However, the 29-gauge needle AS group was associated with a significantly lower blastocyst hatching rate (83.6 % vs. 91.2 %), shorter average gestational duration (37.36 ± 2.34 vs. 38.06 ± 1.76), and higher premature birth rate (40.00 % vs. 21.15 %) compared with Laser pulse AS group.
CONCLUSION: No significant differences in the effectiveness of the two methods applied prior to blastocyst vitrification were observed before birth, while after birth, a significantly improved clinical outcome was obtained with laser pulse AS indicating that this is a more effective pre-processing method for blastocyst vitrification.