Is one cycle of PGS predictive of the next? evidence from embryo banking

Abstract

OBJECTIVE: To determine if vitrification (Vit) can provide improved survival and pregnancy rates compared to a modified slow freeze protocol that had proven very successful for 2PN and multi-cell embryos over the years. DESIGN: Prospective comparison with Vit. performed 3 set days each week vs. 4 for slow freeze. MATERIALS AND METHODS: Vit. protocol: Irvine media, 6-10 minutes in equilibration solution and 90 seconds in vitrification solution at room temperature then loaded onto High security vitrification (HSV) highsecurity straw in<1ul of medium, sealed and plunged. Modified slow freeze equilibrate in modified human tubal fluid + 10% Serum Protein Substitute for 10 minutes, then 1.5M propanediol for up to 20 minutes, then loaded in straw, seeded, and cooled from -6C to -40C at ramp rate 0.4C/min in alcohol bath freezer, then plunged. A comparison of survival and cleavage rates were performed and 2 embryo stages were also compared – 2 pronuclear and day 3 cleavage stage. RESULTS: Vit. vs. slow freeze 2PNs – Vit. 35/36 (97.2%) survived and 33/ 35 (94.3%) cleaved to more than 1 cell. Slow freeze 92/96 (95.8%) survived and 87/92 (94.6%) cleaved. Vit. vs. slow freeze for day 3 cleaved embryos – (50% blastomere survival) – Vit. 65/71 (91.5%) vs. slow – 40/45 (72.7%) survived (p1⁄4< .05, chi-square). Cleaving – Vit. 59/65 (90.7%) vs. slow 38/40 (95%). Clinical pregnancy rate – 2PN – Vit. – /4 (75%) with implantation rate of 50% (4/8), slow freeze – 8/15 (53.3%) with 30% (10/30) implantation rate. Clinical pregnancy rate – multi-cell Vit. – 8/17 (47.1%) with implantation rate of 12/16 (75%). The only comparison with a statistically significant difference was implantation rate of multi-cell embryos with p< .05, Fisher’s exact test in favor of Vit. Slow – 6/13 (46.2%) with implantation rate of 7/23 (30.4%). CONCLUSION: The results seem comparable between the two techniques with a possible advantage of Vit. Over slow for survival of day 3 multi-cell embryos. The slow freeze process is less expensive. There is not a great deal of studies on the efficacy of Vit. at the 2PN stage. The modified slow freeze is different from the standard Lassalle-Testart slow freeze protocol.