A Comparison of Blastocyst Slow Freeze and Vitrification in Frozen Blastocyst Transfer

Abstract

OBJECTIVE(S): To evaluate the blastocyst vitrification technique and the slow freezing technique with regard to survival rate and clinical pregnancy rate. DESIGN: Retrospective clinical study of frozen blastocyst transfer (FBT) cycle outcomes comparing slow freeze and vitrification. MATERIALS AND METHOD(S): We performed 120 cycles of FBT between January 2005 and October 2008. Before March 2007, blastocysts were frozen using a freeze control Cryo bath and Irvine Scientific blastocyst freezing media. From March 2007, all blastocysts were vitrified using the Irvine Scientific Cryo Tip closed system. Blastocysts were cultured in SAGE blast media before transfer. Blastocyst transfers were performed in hormone replacement cycles. All transfers were performed under standard conditions using ultrasound guidance. RESULT(S): There was no significant difference between the group receiving slow freezing blast and those receiving blast virtification for the number transferred (χ2 = 0.48, P=.49) and pregnancy rate (χ2 = 0.29, P=.59). However, there was a significant difference in %NT (χ2 = 5.32, P=.02) and survival rate between the two groups (χ2 = 10.17, P=.001). The group receiving blast vitrification had a higher proportion of transfer and survival. CONCLUSION(S): Vitrification with the cryo tip is an efficient, fast, simple procedure for freezing blastocysts. These results indicate that vitrification of human blastocysts provides a safe and viable alternative to current slow freezing protocols. This study shows that the Cryo Tip vitrification method provides a better survival rate that should result in a better clinical outcome. Vitrification of blastocysts is our standard protocol for cryopreservation.TableAge, yearsGroupNo. of cyclesNo. of cycles transferred% No transferClinical pregnancy rate, %Survival rate, %Average no./FBT35.7A, slow freezing of blastocysts100937%35 (33/93)71 (237/335)2.5135.9B, vitrification of blastocysts20200%45 (9/20)92 (54/59)2.45 Open table in a new tab