This research investigated the impact of re-freezing embryos at different growth stages on their ability to develop. They studied re-vitrified human embryos in a clinical setting and also used mouse embryos for lab experiments. The results showed that re-freezing embryos at the blastocyst stage after initially freezing them at the 8-cell stage lowered the success rate of pregnancies. However, when embryos were frozen twice at the 8-cell stage, the pregnancy outcomes were similar to those frozen only once. The experiments also revealed that re-freezing embryos increased the levels of certain proteins associated with cell death. Overall, re-freezing embryos at different stages can affect the chances of successful pregnancies, especially when done at the blastocyst stage following an initial freeze at the 8-cell stage.