The paper that presented in Asia Pacific Initiative on Reproduction 2012 (ASPIRE)
Safe Fertility Center, Bangkok, Thailand
Objective : To compare the survival and pregnancy rates after transfer of blastocysts cryopreserved by either vitrification or slow freezing.
Design : Retrospective study.
Setting : Safe Fertility and PGD Center.
Patients : Blastocysts from unselected infertility patients (age: 20 to 53 years, average 37.6 years) were produced by in vitro fertilization or ICSI. PGD was regarded as an exclusion criterion. Stimulations and oocyte-embryo handling protocols were identical for the two groups. All embryos were cryopreserved in the 5th or 6th day after oocyte retrieval. The average age patients, the average number and quality of transferred blastocysts did not differ between the two groups.
Intervention : Blastocysts were vitrified by using the Crytop method, carrier tools and solutions were obtained from Kitazato Ltd (Fujinomiya, Japan). For traditional slow freezing, blastocysts were cryopreserved in standard 0.25 ml insemination straws using propanediol and sucrose as cryoprotectants (Cook, Sydney IVF).
Main Outcome Measures : Survival rate, ie. clearly visible reexpansion of the blastocel after crygpreservation; and pregnancy rate. Corresponding values were evaluated with the T-Test and Chi Square Tests, respectively. Differences with’P values lower than 0.05 were regarded as significant.
Results : Cycles were performed between January, 2008, and October, 2011. Survival and pregnancy rates for 85 vitrification versus 75 slow freezing cycles were 96.22 and 45.53% versus 82.37 and 25.33%, respectively, Corresponding values between the two groups were significantly different (P < 0.05).
Conclusions : Cryotop vitrification of Day 5 to 6 blastocysts results in higher survival and pregnancy rates than a commonly applied slow freezing protocol.