A baby boy has been born after being conceived with sperm frozen for 21 years in what scientists say is a new record.
The boy's father had his sperm frozen when he was 17 before starting successful treatment for testicular cancer in the early 1980s.
The man's sperm was stored in liquid nitrogen about two decades ago and was not thawed until he married and decided to start a family.
Scientists injected a single sperm into the mother's eggs in a technique called intractoplasmic sperm injection (ICSI) to create embryos. The boy was born two years ago following four attempts at in vitro fertilisation (IVF).
"I'm 99 percent sure that it is the oldest frozen sperm sample used [for a live birth]," said Mr Greg Horne, a senior embryologist at St Mary's Hospital in Manchester, which treated the baby's parents.
"Even after 21 years of storage, the percentage of motile sperm after thawing was high," said Mr Horne, who reported the case in the journal Human Reproduction.
Although there have been suggestions that freezing and thawing can damage DNA in sperm, Mr Horne said there was no evidence that damage was increased by the length of time the sperm was stored.
The man and his wife, who chose to remain anonymous, wanted their case publicised to encourage young cancer patients to have hope for the future.
Young men diagnosed with cancer may become infertile following treatment but they can store sperm beforehand. In Britain sperm can be stored until the man reaches 55.