Vitrification is a method for freezing embryos that is better than slow freezing because it reduces the risk of ice-related damage and is simpler and faster. However, the solution used for vitrification must contain high levels of certain chemicals that can be harmful. Different solutions have been developed over time, with ethylene glycol being the most common now. Embryos can be frozen using either traditional methods with straws or ultra-fast methods with tiny tools. The ultra-fast method is better because it uses less harmful chemicals.