Women who have used assisted reproductive technologies (ART) are over a third more likely to develop ovarian cancer than other women, a large-scale study finds.
But researchers said it is likely the increased risk reflects underlying health problems in women who need help conceiving, rather than being a result of the treatment itself.
Lead researcher on the study, Alastair Sutcliffe from the Institute of Child Health at University College London, told the Daily Mail: 'This internationally-unique study suggests little for women to worry about regarding the risk of cancers and the drug treatments they undergo to have a baby with IVF.'
The study is the largest of its kind and was presented at the 71st Annual Meeting of the American Society for Reproductive Medicine in Baltimore. It was a registry study based on records from the Human Fertilisation and Embryology Authority and included all women who underwent ART in the UK between 1991 and 2010, totalling more than 250,000 women and 2.2 million years of observation.
The nature of the study does not allow conclusions about cause and effect, but several aspects suggest the increased risk may not be related to the treatment itself.
The researchers found that infertility due to 'female factors', such as endometriosis, was particularly associated with a higher cancer risk, and those who did not have a live birth following ART had the highest risk.
By contrast, when infertility was due to factors in the male partner only, there was no increased risk of cancer compared to the general population. Furthermore, risk did not increase with the number of treatment cycles.
But other findings from the study did suggest treatment could play a role. For instance, the risk of developing ovarian cancer was greatest for younger women and in the first three years following ART.
Although the relative risk of ovarian cancer was increased by 37 percent compared to the general population, the risk remains small in absolute terms: 15 out of 10,000 women who had received ART developed ovarian cancer compared with 11 out of 10,000 women in the general population.
The study is not the first to establish an association between ART treatments and cancer, and several theories have speculated about the possible causes. One theory suggests the use of hormonal drugs in the treatments may increase the risk of cancer directly.
Another possibility is that stimulation of the ovulatory process itself may render women more susceptible to developing cancer, as ovulation appears to be necessary to develop ovarian cancer.
'This study, from a huge database, suggests that women who have IVF with certain conditions, such as endometriosis, may be at increased risk of developing ovarian cancer,' Professor Balen told the Telegraph.
'The question remains as to whether women who have received IVF treatment should be offered surveillance/screening and, if so, how often and by what means.'