Sluggish freeze versus microfreeze
Successful freezing and thawing of reproductive tissue first occurred in the 1950s. The method implemented at the time, which we now call "slow freezing", is still used today in every reproduction laboratory. The method combines two protective aspects that work together to prevent the formation of ice crystals in the cells: adding a cryoprotective solution to the sample, which replaces the water in the cell, after which the cells are subjected to a progressive, controlled temperature drop. If we look at an ice crystal up close, it consists of sharp edges that can tear through the cell membrane. This slow freezing method results in 50% survival of the cryopreserved cells. This is more than sufficient for a normal healthy sperm count, and even if the sperm count is lower than normal, survival is usually sufficient for fertility treatment. However, this was nowhere near enough to be used effectively on eggs and embryos, and this problem prompted further investigation. As a result, a method called glazing was developed in the 1980s. This procedure uses a higher concentration of cryoprotectant and a rapid, almost instantaneous drop in temperature. This gives a survival rate of about 90% and has become the standard practice for egg and embryo cryopreservation.
Maze adapted this method of vitrification for our sperm freezing protocol. The small volume required to achieve instant cell freezing means this technique can freeze several hundred sperm at a time. This makes it an excellent option for someone with very low sperm counts who knows that their best option is IVF-ICSI.
Curious about a method or concerns about sperm conservation? Contact us today for a free consultation. We're here to help.