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

Abstract

ObjectiveThis study was an observational retrospective cohort, with the objective to compare oocyte cryopreservation efficiency between slow freezing using choline chloride based medium, and vitrification protocol using cryotop.DesignA total of 101 cycles (slow freezing and vitrification techniques) were performed for those patients that decided to thaw their oocytes from 2009 to 2011.Materials and MethodsAll patients with at least 10 oocytes and not willing to freeze embryos were offered the possibility to cryopreserve oocytes. The oocytes cryopreserved by slow freezing followed Stachecki's (1998) protocol, while the oocytes vitrified 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. Two days before the replacement of the embryos, the oocytes were thawed. After thawing, the oocytes were kept in a incubator during 2 hours before inseminating by ICSI. The survival, fertilization, cleavage, average embryo transfer and pregnancy rates were compared through the chi-square test (P<0.05).ResultsTable 1Outcome results from slow freezing versus vitrification protocol.Slow freezing (%)Vitrification (%)Cycles5645Oocytes Thawed523399Oocytes Survived*P=0.0085289 (55.2)255 (63.9)Oocytes Fertilized200 (69.2)177 (69.4)Embryos Cleaved185 (92.5)156 (88.1)Embryos Transferred121 (65.4)100 (64.1)Average Embryo Transfer2.22.2Implantation15 (12.4)16 (16.0)Pregnancies16 (28.6)15 (33.3)Clinical Pregnancies14 (25.0)13 (28.9)* P=0.0085 Open table in a new tab ConclusionAlthough the survival rate was statistically higher for the vitrification technique, this did not result in a statistically higher implantation and/or pregnancy rate. Therefore both techniques are reliable to cryopreserve oocytes. ObjectiveThis study was an observational retrospective cohort, with the objective to compare oocyte cryopreservation efficiency between slow freezing using choline chloride based medium, and vitrification protocol using cryotop. This study was an observational retrospective cohort, with the objective to compare oocyte cryopreservation efficiency between slow freezing using choline chloride based medium, and vitrification protocol using cryotop. DesignA total of 101 cycles (slow freezing and vitrification techniques) were performed for those patients that decided to thaw their oocytes from 2009 to 2011. A total of 101 cycles (slow freezing and vitrification techniques) were performed for those patients that decided to thaw their oocytes from 2009 to 2011. Materials and MethodsAll patients with at least 10 oocytes and not willing to freeze embryos were offered the possibility to cryopreserve oocytes. The oocytes cryopreserved by slow freezing followed Stachecki's (1998) protocol, while the oocytes vitrified 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. Two days before the replacement of the embryos, the oocytes were thawed. After thawing, the oocytes were kept in a incubator during 2 hours before inseminating by ICSI. The survival, fertilization, cleavage, average embryo transfer and pregnancy rates were compared through the chi-square test (P<0.05). All patients with at least 10 oocytes and not willing to freeze embryos were offered the possibility to cryopreserve oocytes. The oocytes cryopreserved by slow freezing followed Stachecki's (1998) protocol, while the oocytes vitrified 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. Two days before the replacement of the embryos, the oocytes were thawed. After thawing, the oocytes were kept in a incubator during 2 hours before inseminating by ICSI. The survival, fertilization, cleavage, average embryo transfer and pregnancy rates were compared through the chi-square test (P<0.05). ResultsTable 1Outcome results from slow freezing versus vitrification protocol.Slow freezing (%)Vitrification (%)Cycles5645Oocytes Thawed523399Oocytes Survived*P=0.0085289 (55.2)255 (63.9)Oocytes Fertilized200 (69.2)177 (69.4)Embryos Cleaved185 (92.5)156 (88.1)Embryos Transferred121 (65.4)100 (64.1)Average Embryo Transfer2.22.2Implantation15 (12.4)16 (16.0)Pregnancies16 (28.6)15 (33.3)Clinical Pregnancies14 (25.0)13 (28.9)* P=0.0085 Open table in a new tab ConclusionAlthough the survival rate was statistically higher for the vitrification technique, this did not result in a statistically higher implantation and/or pregnancy rate. Therefore both techniques are reliable to cryopreserve oocytes. Although the survival rate was statistically higher for the vitrification technique, this did not result in a statistically higher implantation and/or pregnancy rate. Therefore both techniques are reliable to cryopreserve oocytes.