To examine the viability and re-expansion of expanded blastocysts in conjunction with the ultra rapid vitrification and consider the effectiveness of artificial shrinkage (AS). Retrospective The materials examined were 179 cycles that were carried out with AHA and embryo transfer (ET) after freezing - thawing embryos that developed to the blastocyst stage from January 2003 to December 2004 with vitrification using a cryoloop, and on 25 cycles carried out with AHA after freezing - thawing with vitrification after carrying out AS on extra expanded blastocysts that had been judged to be of a grade not appropriate for frozen ET. The blastocysts were suspended in solution I, which is HEPES-buffered HTF medium containing 5 mg/ml of HSA (base medium) containing 7.5% DMSO and 7.5% EG at about 37°C. A cryoloop was dipped into cryoprotectant solution II, which is a base medium containing 15% DMSO, 15% EG, 10mg/ml Ficoll 70, and 0.65 M sucrose, at about 37°C, to create a filmy layer of the solution on the loop. 1 min and 45 sec after suspending the blastocysts in solution I the blastocysts were washed in solution II and transferred onto the filmy layer on the cryoloop. Within 30 sec of suspension in solution II, the cryoloop was plunged into liquid nitrogen. To Thaw the blastocysts, placed into a well of the base medium containing 0.33 M sucrose at 37°C. After 2 min, the embryos were transferred to the base medium containing 0.2 M sucrose. After an additional 3 min, the embryos were suspended in base medium for 5 min. AHA was performed after warming. After that, ET was carried out after 5 hours of culturing. In the cases of AS, a micro needle was inserted from a position whereby the ICM was avoided, and the blastocoele was shrunk. Among the embryos for which ET was carried out, the clinical pregnancy rates (FHM) of the group that did not include blastocysts expanded before freezing was 39.1% (34/87), and the group that included expanded blastocysts was 53.7% (22/41), and for the group with only expanded blastocysts the rate was 58.8% (30/51), and the rate for group with only expanded blastocysts was significantly higher. In the group with only expanded blastocysts, the FHM rates of the group that did not include re-expanded blastocysts after thawing was 22.2% (2/9), the group that included re-expanded blastocysts was 66.7% (6/9), and the group with only re-expanded blastocysts was 66.7% (22/33), so the rate of the group with only re-expanded blastocysts was significantly higher. Re-expanded rates were; the group with AS (-) was 47.4% (45/95), and the group with AS (+) was 76.5% (17/25), so the group with AS (+) tended to have a higher rate Our analysis suggests that that FHM rate of blastocysts expanded before freezing is higher, and the FHM rate becomes even higher when re-expansion after thawing is observed. Also, it was found that the re-expansion rate of expanded blastocysts showed a tendency to be higher in spite of them being expanded blastocysts that were not a suitable grade for freezing when AS had been carried out. As a consequence of these results, it seems that carrying out AS on expanded blastocysts can improve their re-expansion rates, and it suggests that an increase of the FHM rate can be achieved, and we found that AS is an effective technique.