Even low doses of radiotherapy to the head slightly up infertility risks in women, according to new research.

Scientists have known that high doses of radiation to the brain to kill tumors, above 30-35 Gy, likely destroyed cells in the hypothalamus and pituitary gland that produce hormones which control sexual development and pregnancy.

But a study published last week in the journal Fertility and Sterility shows even modest doses, around 22-27 Gy, slightly increase the risk of infertility.

In the current study, researchers, led by Dr. Daniel Green, an oncologist with the St. Jude Children's Research Hospital in Memphis, compared the fertility of women who were treated for cancer as children with that of their sisters.

They looked at 3,619 cancer survivors diagnosed between 1970 and 1986 who received radiation to the brain, but none or nearly none to the ovaries (as that can also induce infertility), before they were 21, and their 2,081 untreated siblings.

As a group, cancer survivors were essentially as likely to report being pregnant as their siblings, the authors said. However, statistical analyses suggested that women who had received radiation doses to the hypothalamus-pituitary axis of at least 22 Gy had about one-third fewer pregnancies than cancer survivors who weren't treated with radiation, according to a Reuters Health report.

Slightly more than half of the children in the study had been diagnosed with leukemia or brain cancer. Although this sort of radiation therapy isn't as commonly used now as it once was for leukemia, there are still many women who received treatment a decade or so ago who could be at risk for fertility problems, according to the researchers.

In a poster presentation based on similar research share at The American Society for Radiation Oncology's meeting last October, Green suggested low-dose radiotherapy could affect fertility by causing luteal phase deficiency, which interferes with ovulation.

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