Reproductive Factors May Not Protect Against Ovarian Cancer in Younger Generations

A study of over 2 million Korean women suggests the protective effect of having two or more children against ovarian cancer may be diminishing in younger birth cohorts.

Published on Feb. 12, 2026

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A nationwide study of more than 2 million South Korean women examined how reproductive factors influence the risk for ovarian cancer across different generations and menopausal stages. The study found that while having two or more children reduced the risk for ovarian cancer by 32% in women born in the 1930s through 1950s, it showed no significant protective effect in women born in the 1960s. The authors suggest this is due to Korea's rapid fertility decline, with the 'two or more' births category in the 1960s cohort usually meaning only two or three children, compared to four or more in earlier generations.

Why it matters

The findings call into question whether having two or more children is still protective against ovarian cancer, especially in populations experiencing declining fertility rates. Understanding how reproductive factors influence ovarian cancer risk in different generations is crucial for developing tailored prevention strategies.

The details

The study tracked 2,285,774 women aged 40 years or older for more than a decade, identifying 10,729 ovarian cancer cases. Researchers found that, compared with nonparity, having two or more children reduced the risk for ovarian cancer by 32% in women born in the 1930s through 1950s, but showed no significant protective effect in women born in the 1960s. The authors suggest this is due to Korea's rapid fertility decline, from above 4.0 in the early 1970s to 0.72 in 2022, compressing reproductive shifts into a single generation. They note that in earlier, high-fertility generations, parity of two or more often meant four or more births, creating a wider gap in ovulation exposure compared to women who had no children. But in the 1960s cohort, women in the 'two or more' births category usually had only two or three children.

  • The study tracked women aged 40 years or older for more than a decade, from an unspecified start date.

The players

Christos Evangelou

A freelance medical writer and science communications consultant.

Barbara A. Goff, MD

A professor and chair of the Department of Obstetrics and Gynecology at the School of Medicine, University of Washington, Seattle.

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What they’re saying

“I think this hypothesis is very plausible. Prior to the 1960s, average family size was larger, and women were having four babies or more. Whereas after the 1960s, the size of families started to dramatically decrease, so the length of exposure to pregnancy declined significantly.”

— Barbara A. Goff, MD, Professor and chair of the Department of Obstetrics and Gynecology at the School of Medicine, University of Washington, Seattle (JAMA Network Open)

What’s next

The authors emphasized that prevention strategies are even more critical in countries where women have fewer children, since their study shows that traditional protective factors such as high parity may no longer apply in younger, low-fertility populations. Understanding family history and pursuing genetic testing, as well as considering risk-reducing surgery like bilateral salpingectomy, are important steps for identifying and protecting high-risk women.

The takeaway

This study highlights the need for population-specific prevention strategies, as the protective effect of reproductive factors against ovarian cancer may be diminishing in younger generations experiencing declining fertility rates. Clinicians should be aware of these changing patterns and focus on early symptom recognition and tailored screening approaches to combat the rising threat of ovarian cancer in low-fertility populations.