Which statement about embryo cryopreservation is correct?

• A. Slow-freezing minimizes ice crystal formation.
• B. Vitrification is rapid freezing that minimizes ice crystals and improves survival.
• C. Both methods are identical in outcome.
• D. Cryopreservation is no longer used.

Answer: (B)

Prevention of ice crystal formation during freezing is what preserves embryo viability. Vitrification achieves this by using very high concentrations of cryoprotectants and extremely rapid cooling, so the water inside the cells turns into a glass-like, solid state instead of forming ice crystals. This avoids the mechanical damage to membranes and the osmotic stress that ice crystals cause, resulting in higher survival after thaw and reliably good pregnancy outcomes.

Slow-freezing cools more gradually, which allows ice crystals to form either inside cells or in the surrounding fluid. Those crystals can puncture membranes and disrupt cellular integrity, lowering post-thaw survival compared with vitrification. The idea that both methods yield identical results isn’t accurate because vitrification tends to have superior survival and typically comparable or better pregnancy rates. Cryopreservation remains a standard, ongoing practice in fertility clinics, not something that’s no longer used.

So the statement that vitrification is rapid freezing that minimizes ice crystals and improves survival is the best description.