Small breaks in the DNA of a man's sperm may contribute to reduced pregnancy rates following IVF, according to research at Queen's University, Belfast, which has also identified this as the cause of many cases of unexplained infertility.

Scientists looked at 203 couples undergoing and 136 couples undergoing ICSI and divided them into three groups based on how much DNA damage was present in the man's sperm. Using a new test for male infertility, the researchers found that in 80 percent of couples with 'unexplained infertility' high sperm damage was the cause.

The study also found the amount of sperm damage is related to the chances of having a baby following IVF. The results showed that couples in which the men had less than 25 percent DNA damage had a much higher chance of successfully conceiving a child, compared with men who had up to 50 percent damage.

'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 infertility"', said Professor Sheena Lewis, from the School of Medicine, Dentistry and Biomedical Sciences at Queen's University Belfast, who led the research. 'In our study, we have now had a breakthrough which explains the cause of infertility for many of those couples', she added.

Infertility affects around one in six couples trying to conceive and it is estimated that male infertility contributes to nearly half of all cases. Until now, many fertility clinics have assessed sperm quality based on criteria such as sperm count, motility, and shape, while the underlying cause of any obvious defects has remained unknown.

The researchers in this study, however, used a comet assay test called SpermComet to detect faulty DNA in sperm, which can be damaged by a number of factors including poor diet and smoking, and can contribute to impaired embryo development, miscarriage, and birth defects.

Professor Lewis said the study offers hope to those couples with 'unexplained infertility'. 'These couples often invest a lot of time and money in fertility treatments like intra-uterine insemination which are unlikely to be successful', she said.

'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'.

Christopher Barratt, professor of reproductive medicine at the University of Dundee, told the BBC: 'the question is whether this type of testing is going to help and that is where the evidence needs to be stronger'.

The study was published in the journal Reproductive Biomedicine Online.

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.