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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 partners and couples with fertility issues who made need a sperm donation. A number of factors contribute to how long frozen semen stays viable, and time alone is not usually a major concern. Frozen semen will generally remain viable for an extended length of time as long it is frozen properly to begin with and not thawed and refrozen.
The initial strength of the sperm affects the viability of frozen semen more than the length of the time that it is frozen. Strong and healthy sperm will remain viable for a longer period of time than weak and unhealthy sperm. Additionally, each man's sperm will react differently to being frozen; up to 20% of men have sperm that does not freeze well, and which will not survive being 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 is difficult to predict how long correctly frozen and stored semen will remain viable. Some experts recommend frozen sperm be used within 12 years, however, for the best chances that it will be viable. In the early 2000s, a baby was born who had been conceived with semen that was frozen 21 years previously. Studies have also indicated that children born from sperm that had been frozen seem to be just as healthy as other children.
The procedure of freezing sperm 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 frozen gradually in extremely cold temperatures; typically, this begins with the vapor of liquid nitrogen. 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 must not be exposed to room temperature for more than a few seconds before being placed in a warm water bath at body temperature — 98°F (37°C) — for several minutes. During the 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.