A semen sample, produced via masturbation, will be analyzed in a lab for sperm count, motility (what percentage of sperm are moving or “swimming”), and morphology (what percentage of sperm are the correct size and shape). This is important because you don’t want to undergo semen freezing without first checking the health of your sperm.
High-quality labs will also perform a “post-thaw analysis” before sperm freezing. In this procedure, a very small portion of your sperm will be frozen, thawed, and re-assessed for quality. This helps determine if your sperm are suitable for storage and estimates how many sperm will survive the process of freezing and thawing. Sperm will be “washed” and processed to remove semen proteins and contaminants, and concentrate sperm.
Just before sperm freezing, the lab scientist will add cryoprotectant, a substance that prevents damaging ice crystals from forming inside sperm. (This cryoprotectant doesn’t impair the quality of your sperm.) Finally, vials of sperm will be plunged into liquid nitrogen to bring them down to -196ºC. This is the temperature at which biological activity pauses.
Once your sperm are frozen, their health and quality are maintained. Sperm can be stored indefinitely, with no significant impact on their ability to create a pregnancy.