Study Suggests Shifting Reproductive Patterns Are Reshaping Ovarian Cancer Risk

Ovarian Cancer and the Changing Landscape of Women’s Health

Ovarian cancer remains one of the most challenging gynecologic cancers, with its risk strongly influenced by a woman’s reproductive history. Yet as societies undergo rapid demographic changes—like falling birth rates and later childbearing—the classic risk factors may no longer apply in the same way for all generations. A new, large-scale Korean study dives into how reproductive factors such as age at menarche, number of births, breastfeeding, and hormone use affect ovarian cancer risk across menopausal status and birth cohorts.

The Study: Tracking Risks in Over Two Million Women

Drawing on health data from more than 2.2 million Korean women aged 40 and above, researchers followed participants for an average of nearly 11 years. They examined how reproductive factors—including the age at first period (menarche), number of children, breastfeeding duration, use of oral contraceptives (OC), age at menopause, reproductive lifespan, and hormone replacement therapy (HRT)—impacted ovarian cancer risk. Importantly, they looked for differences between pre- and postmenopausal women and among women born in different decades.

Key Findings: Not All Generations Are the Same

Early menarche (first period at age 12 or younger) increased ovarian cancer risk for both pre- and postmenopausal women.

More births (two or more) lowered risk in both groups, but this protective effect was less pronounced—or even absent—in women born in the 1960s compared to older generations.

Longer breastfeeding (12+ months) and OC use (1 year or more) reduced risk, but only for premenopausal women.

For postmenopausal women, later menopause, longer reproductive span, and use of HRT were linked to increased ovarian cancer risk.

Generational shift: As fertility rates dropped dramatically in Korea, the protective benefits of high parity (more children) appear to wane in recent birth cohorts.

Implications: Tailoring Cancer Prevention for a New Era

The study highlights that classic ovarian cancer protection from higher numbers of births doesn’t apply as strongly in today’s low-fertility societies. As younger generations have fewer children, and with changing breastfeeding and contraceptive patterns, prevention strategies may need to be rethought. Understanding these generational differences is vital for doctors and policymakers aiming to reduce ovarian cancer risk in aging, low-fertility populations.

5 Key Takeaways:

Early menarche and later menopause both increase ovarian cancer risk.

Having two or more children lowers risk, but less so in more recent birth cohorts.

Breastfeeding and oral contraceptives only lower risk in premenopausal women.

Hormone replacement therapy for 2–5 years increases risk in postmenopausal women.

Public health strategies must adapt to generational changes in reproductive patterns.

Citation:

Kim JH, Hwang I-S, Lee S-J, et al. Reproductive Shifts and Ovarian Cancer Risk in Women Aged 40 Years or Older. JAMA Network Open. 2026;9(2):e2556840. doi:10.1001/jamanetworkopen.2025.56840