New research has given fresh hope to couples diagnosed with 'unexplained infertility'.
A study of 239 couples with unexplained fertility found high sperm DNA damage in 80 per cent of the couples trying to conceive.
Currently, some 50,000 couples require fertility treatment in the UK every year, but up to one third of these are diagnosed with unexplained or idiopathic infertility, as tests are unable to find a cause for the problem.
The researchers from Queen's University Belfast said the discovery will lead to better treatment for couples, saving them time, money and heartache.
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Professor Sheena Lewis from the School of Medicine, Dentistry and Biomedical Sciences said: "For almost one third of couples, until now, there has been no obvious cause for infertility and these couples are given the diagnosis of ‘unexplained fertility’.
"These couples often invest a lot of time and money in fertility treatments like intrauterine insemination (IUI) unlikely to be successful.
"In our study we have now had a breakthrough which explains the cause of infertility for many of those couples.
"Now that we have found the cause of infertility for these couples suitable treatments can be tailored for them which will direct them straight to the best treatment and increase their chances of having a baby.”
The study is also the first to show that the chances of having a baby after IVF is closely related to the amount of DNA damage a man has in each of his sperm, said the researchers, who have developed a test which measures this.
Professor Lewis said: “With one million couples worldwide requiring fertility treatment, these new research findings will give many fresh hope of having a family.”
The study is published in the journal Reproductive Biomedicine Online.