Infertile women are at greater risk of getting cancer, according to researchers.
A study has found that women with fertility problems are 18 per cent more likely to get cancer, in particular womb and ovarian cancers.
That may be because women who need IVF are given powerful drugs which alter their hormone levels.
Infertile women may also have genetic problems which raise their risk of cancer as well as childlessness.
Researchers tracked more than 64,000 women with fertility problems over almost four years, comparing their medical records with those of 3.1 million fertile women.
The results show two per cent of infertile women were diagnosed with cancer in that time, compared to just 1.7 per cent of women without fertility problems.
Dr Gayathree Murugappan, lead author of the study from Stanford University School of Medicine, said: 'We do not know the causes of the increase in cancer that we found in this study - whether it might be the infertility itself, the causes of the infertility, or the infertility treatment.
'We can only show there is an association between them. In the future, we hope that we will be able to understand why infertile women are at higher risk of cancer, for example, by identifying a common, underlying mechanism that can cause cancer and infertility.'
Fears have been raised over the drugs infertile women are given during IVF, which are needed to boost their ovaries so they can produce extra eggs to be fertilised in the laboratory and create a baby.
These change levels of hormones in a woman's body which could help to trigger breast, ovarian and womb cancers.
The study did not find infertile women had higher rates of breast cancer, but they were 78 per cent more likely to be diagnosed with womb cancer and 64 per cent more likely to get ovarian cancer.
Female sex hormones have also been linked by some experts to liver cancer, and infertile women were 59 per cent more likely to get liver or gallbladder cancer.
The study, published in the journal Human Reproduction, states that infertile women may be at greater risk of cancer regardless of whether they undergo IVF.
They may be unlucky enough to have mutations in genes important for DNA repair which cause both fertility problems and cancer.
Or it may be that being unable to conceive a child is the first sign that a woman has cancer, and that it has simply not yet been detected.
However, having a baby may be the solution for women wanting to reduce their risk of cancer.
The study found infertile women who managed to get pregnant and had a child saw their danger of ovarian, womb, lung, liver and gallbladder cancers fall to around the same level as fertile women.
Having a baby also has an effect on hormones linked to some types of cancer.
The study found the greater risk of womb cancer seen in infertile women may be explained by some infertile women having polycystic ovary syndrome.
The researchers also stress that infertile women's increased cancer risk is still small, with senior author Dr Michael Eisenberg stating: 'The low overall incidence of cancer among these women means that one in 49 infertile women would develop cancer during the follow-up period compared to one in 59 women in the women who were not infertile.'
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