By Stephanie Stahl

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PHILADELPHIA (CBS) – New research finds a link between breast cancer and childbirth. This has a lot of people worried because for years doctors have said childbirth is protective against breast cancer.

Researchers are now saying having children does still guard against breast cancer but it can take more than two decades for the protective benefits to be seen.

Women who have babies may face a greater chance of breast cancer compared to women who don’t have children.

Researchers from the University of North Carolina found the increased risk lasts for decades from the time of the woman’s last child.

It’s highest being five years after the child is born and it continues for 24 years with the risk at 80 percent but then 34 years after childbirth, the risk of breast cancer actually goes down 23 percent.

Doctors say that’s an important point since most breast cancers happen in women over age 60.

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So if you look cumulatively it decreases the risk because breast cancer is relatively rare in young women,” said Dr. David Agus.

The study also found the increased risk of breast cancer after childbirth was higher for women who were older when they had their first child for women who also had a family history of the disease and for women who had a higher number of births.

“This does change our screening criteria and now we’re going to ask when was your last child to determine if you should be screened or not,” said Dr. Agus.

Researchers say breastfeeding did not impact the results either way.

Health experts don’t know why the risk goes up for 24 years after childbirth but they think the estrogen surge during pregnancy may be a factor, but the overall risk is still low.

Stephanie Stahl