The more times women give birth, the lower their risk of ovarian cancer—maybe because of the changes in hormone levels that occur during pregnancy. A group of University of Southern California researchers asked several hundred ovarian cancer survivors and women who'd never had ovarian cancer about their hormonal history, and found something surprising about births.

What the researchers wanted to know: How do various hormonal factors affect the risk of ovarian cancer?

What they did: The researchers found women through a Los Angeles County cancer registry and contacted them thnrough their physicians for an interview. They intervewed 477 ovarian cancer patients and, when they could, also matched each to a control in her neighborhood of the same race and ethnicity and roughly the same age. All of the women were asked about their medical and personal histories, including questions about births and hormone use.

What they found: The researchers found some well-known risk factors, like family history of ovarian cancer or using talcum powder on their genitals, but also one surprise: age at last birth. Women who had their last child when they were older had a lower risk of getting ovarian cancer. Compared with women who'd never had a child, a woman who had her last baby after age 35 had a 58 percent lower chance of ovarian cancer, while a woman who had her last baby before she turned 25 had only a 16 percent lower risk.

What the study means to you: All things considered, this isn't a good reason to delay giving birth or keep having babies—the study is more useful as information to use in calculating someone's risk or to help understand what causes ovarian cancer.

Caveats: These results are new and somewhat iffy, so don't go making major life decisions based on them.

Find out more: An explanation of ovarian cancer: www.4woman.gov

Read the article: Pike, M.C., et al. "Hormonal Factors and the Risk of Invasive Ovarian Cancer: A Population-Based Case-Control Study." Fertility and Sterility. July 2004, Vol. 82, No. 1, pp. 186–195.

Abstract online: www.fertstert.org