Cryopreserving human embryos at the blastocyst stage can improve pregnancy rates compared to freezing them at an earlier stage. A study found that blastocysts had a 100% survival rate after freezing/thawing, while early embryos had a 59% survival rate. Pregnancy rates after transferring frozen blastocysts were significantly higher at 16.4% compared to 6.2% for early embryos. This shows that freezing embryos at the blastocyst stage can help increase the chances of pregnancy after cryopreservation.