31 Days, 31 Things You Didn't Know About Breast Cancer

The link between having children and the risk of breast cancer is fairly complex. This is because a first pregnancy has two effects on breast cancer risk--one that typically raises risk over the short term and another that lowers risk over the long term.

Women who are over age 35 when they have their first child have a slight increase in lifetime risk of breast cancer compared to women who don’t have children and women who have their first child at younger ages.

Why this differing effect with age? We don’t know for sure, but there are several possible reasons. One reason relates to breast cells. During pregnancy, breast cells grow rapidly. And if there is any genetic damage in the breast cells, it is copied as the cells grow. This increases genetic damage in the cells, which can lead to breast cancer. Because the chance of having such genetic damage goes up with age, women who have their first child at a later age may have a higher risk of breast cancer than younger women.