Is there any difference in vitrification and slow freezing protocol for embryo cryopreservation?

Abstract

This study was an observational retrospective cohort, with the objective to compare the cryopreservation efficiency between slow freezing and vitrification technique using cryotop. A total of 181 cycles were performed for those patients that decided to thaw their embryos from 2009 to 2011. Considering that for the past three years, the embryos have being vitrified in our clinic, we have had the opportunity to thaw embryos either vitrified or frozen by the slow freezing protocol. The embryos cryopreserved by slow freezing followed the traditional protocol with 1.5M of PROH and 0.1M of Sucrose. The embryos cryopreserved by vitrification followed Kuwayama's (2005) protocol. The endometrium was prepared using Estradiol Benzoate with an initial dose of 2mg/day, starting on the 3rd day of the cycle. The maximum dosage used was 6mg/day when the endometrium reached a thickness of 8mm by ultrasound. Three days before the embryo transfer, the patient started using 90mg progesterone gel daily. After thawing, the embryos were kept in a 5% CO2 incubator, humidified in air, at 37°C during 2 hours before transferring. The embryo transfers were performed with a catheter, under ultrasound control. The survival, average embryo transfer, implantation and pregnancy rates were compared through the chi-square test (P<0.05). The results are as follow:Table 1Outcome results from slow freezing versus vitrification protocol.Slow freezing (%)Vitrification (%)Cycles9883Embryos Thawed288226Embryos Survived∗P< 0.0001218 (75.7)206 (91.1)Embryos Transferred213 (97.7)199 (96.6)Average Embryo Transfer2.22.4Implantation22 (10.3)30 (15.1)Pregnancies28 (28.6)29 (34.9)Clinical Pregnancies19 (19.4)25 (30.2)* P< 0.0001 Open table in a new tab Although the survival rate was statistically higher for the vitrification technique, this did not result in a statistically higher implantation and pregnancy rates.