This research looked at using a substance called 1,2 propanediol to freeze human embryos. They froze 85 embryos and then checked how well they survived after thawing. They found that embryos that were 2 days old had a higher chance of surviving than those that were 3 days old. Also, embryos at the 2-, 4-, and 8-cell stages survived better than embryos at other stages. Among certain embryos, 79% had at least half their cells intact after thawing. On average, 19% of all 2-day-old frozen embryos were able to survive after being thawed using 1,2 propanediol. This study shows that the stage and age of the embryo can influence how well it survives the freezing and thawing process.