Semen is collected and frozen for later use for many different reasons. Sperm banks collect semen from donors and freeze the sperm for same-sex couples and couples with fertility problems that necessitated a sperm donation. Several factors contribute to how long frozen semen remains viable, and time alone is usually not a major concern. Frozen semen will generally remain viable for an extended period of time, as long as it is properly frozen and not thawed or refrozen.
The initial strength of the sperm affects the viability of frozen semen more than the length of time it remains frozen. Strong, healthy sperm will remain viable for a longer period of time than weak, unhealthy sperm. Also, each man's sperm will react differently to being frozen; Up to 20% of men have sperm that do not freeze well and will not survive if frozen. Once thawed, some sperm will remain strong while others may decrease in health and become less viable.
Although scientists have been able to freeze semen since the 1950s, modern methods were only really developed in the 1960s, so it's difficult to predict how long properly frozen and stored semen will remain viable. However, some experts recommend using frozen sperm within 12 years for the best chance of viability. In the early 2000s, a baby boy was born who had been conceived with frozen semen 21 years earlier. Studies have also indicated that children born from frozen sperm appear to be just as healthy as other children.
The sperm freezing procedure plays an important role in the preservation and viability of frozen semen for future use. After extensive testing to determine the quality of the sperm, it is divided and placed in vials with a protective compound. Sperm must be gradually frozen to extremely cold temperatures; typically, this starts with liquid nitrogen vapor. The samples are then moved to long-term storage in liquid nitrogen tanks that are at least -321°F (-196°C).
Frozen semen must be carefully thawed to remain viable. When vials are opened, they should not be exposed to room temperature for more than a few seconds before being placed in a warm, body temperature (98°F (37°C)) water bath for several minutes. During thawing, vials must be completely submerged in water to avoid significant temperature loss. After the frozen semen is thawed, it is placed in an insemination device.