A comparison of slow freeze and vitrification in frozen embryo transfer in vitro fertilization

Abstract

OBJECTIVE: Embryo cryopreservation enhances In Vitro Fertilization (IVF) success by allowing the preservation of additional embryos for use in subsequent cycles. Cryopreservation has previously utilized a slow freeze technique. We have used the rapid vitrification technique over the past three years. While vitrification is technically easier, there is limited data on its efficacy. Our objective was to determine whether vitrification is associated with equal or increased success rate in IVF.DESIGN: Retrospective study of Frozen Embryo Transfer (FET) cycle outcomes comparing slow freeze and vitrification techniques performed in a university hospital based IVF program.MATERIALS AND METHODS: We performed 158 cycles of FET between 2003-2007. We thawed 55 sets of slow freeze embryos and 103 sets of vitrified embryos. After a lupron induced or spontaneous menses, incremental dosing of estrace was used in our standard protocol, with progesterone supplementation added prior to day 3-5 of transfer. The slow freeze technique was performed with propylene glycol and sucrose solutions added incrementally. Embryos were incrementally cooled in the Biogenetic planar from 20°C to −30°C over 100 minutes and dropped in liquid nitrogen at −196° C. We thawed slow freeze embryos in a 37° C water bath for 5 minutes and rehydrated them incrementally in propylene glycol and sucrose solutions over 10 minutes. Vitrification technique was performed by dehydrating embryos in Vitrification Solution over 10 minutes. They were rapidly loaded into a straw and plunged into liquid nitrogen −196° C. Vitrified embryos were thawed by placing the straw in a 37° C water bath for 3 seconds followed by a series of post thaw solutions over 13 minutes. T-test and chi square analyses were performed with Systat 10.1.RESULTS: In slow freeze vs. vitrification; there were no differences in the patients' age (34.1 vs. 34.2), FSH (5.8 vs 5.5) or type of infertility. In slow freeze vs. vitrification, embryo survival was 73.1% vs. 88.8% (p< 0.001), chemical pregnancy rate was 32.7% vs. 52.4% (p= 0.018), clinical pregnancy rate was 27.2% vs. 46.6% (p= 0.018), and ongoing pregnancy rate was 20.0% vs. 36.9% (p=0.029). The spontaneous abortion rate was 33.3% vs. 26.0%, not significantly different.CONCLUSIONS: Vitrification was associated with a higher survival rate, and a higher clinical and ongoing pregnancy rate. This supports the continued use of the more rapid and simple vitrification technique. OBJECTIVE: Embryo cryopreservation enhances In Vitro Fertilization (IVF) success by allowing the preservation of additional embryos for use in subsequent cycles. Cryopreservation has previously utilized a slow freeze technique. We have used the rapid vitrification technique over the past three years. While vitrification is technically easier, there is limited data on its efficacy. Our objective was to determine whether vitrification is associated with equal or increased success rate in IVF. DESIGN: Retrospective study of Frozen Embryo Transfer (FET) cycle outcomes comparing slow freeze and vitrification techniques performed in a university hospital based IVF program. MATERIALS AND METHODS: We performed 158 cycles of FET between 2003-2007. We thawed 55 sets of slow freeze embryos and 103 sets of vitrified embryos. After a lupron induced or spontaneous menses, incremental dosing of estrace was used in our standard protocol, with progesterone supplementation added prior to day 3-5 of transfer. The slow freeze technique was performed with propylene glycol and sucrose solutions added incrementally. Embryos were incrementally cooled in the Biogenetic planar from 20°C to −30°C over 100 minutes and dropped in liquid nitrogen at −196° C. We thawed slow freeze embryos in a 37° C water bath for 5 minutes and rehydrated them incrementally in propylene glycol and sucrose solutions over 10 minutes. Vitrification technique was performed by dehydrating embryos in Vitrification Solution over 10 minutes. They were rapidly loaded into a straw and plunged into liquid nitrogen −196° C. Vitrified embryos were thawed by placing the straw in a 37° C water bath for 3 seconds followed by a series of post thaw solutions over 13 minutes. T-test and chi square analyses were performed with Systat 10.1. RESULTS: In slow freeze vs. vitrification; there were no differences in the patients' age (34.1 vs. 34.2), FSH (5.8 vs 5.5) or type of infertility. In slow freeze vs. vitrification, embryo survival was 73.1% vs. 88.8% (p< 0.001), chemical pregnancy rate was 32.7% vs. 52.4% (p= 0.018), clinical pregnancy rate was 27.2% vs. 46.6% (p= 0.018), and ongoing pregnancy rate was 20.0% vs. 36.9% (p=0.029). The spontaneous abortion rate was 33.3% vs. 26.0%, not significantly different. CONCLUSIONS: Vitrification was associated with a higher survival rate, and a higher clinical and ongoing pregnancy rate. This supports the continued use of the more rapid and simple vitrification technique.