This study compared two methods of freezing embryos for use in assisted reproductive technology: vitrification and slow-freezing. Researchers looked at 577 cycles using vitrification and 276 cycles using slow-freezing. They found that vitrification led to more embryos surviving the freezing and thawing process, resulting in higher success rates for implantation, pregnancy, and embryo development. In summary, vitrification is a better method for preserving embryos at the cleavage stage for future use in assisted reproduction treatments.