The link between having children and the risk of breast cancer is complex. It's related to:
A first pregnancy has 2 effects on breast cancer risk. It increases short-term risk and then it lowers long-term risk. The impact of these risks depends on a woman's age at the time of her first pregnancy [6-12].
Women who give birth to their first child at age 35 or younger tend to get a protective benefit from pregnancy [6-11].
Breast cancer risk is increased for about 10 years after a first birth . Then, it drops below the risk of women who don't have children .
The younger you are when you have your first child, the younger you are when you get the protective effect of pregnancy [8-9].
Women who give birth to their first child at later ages have a higher risk of breast cancer compared to women who have their first child at younger ages [6-12].
For example, women who give birth for the first time after age 35 are about 40 percent more likely to get breast cancer than women who have their first child before age 20 . For these women, the increased risk from a first pregnancy is never fully offset by its long-term protective effect .
Women who are over age 35 when they give birth to their first child also have a small increased lifetime risk of breast cancer compared to those who never give birth .
One possible reason for the different effects of age at first childbirth relates to breast cells.
During pregnancy, breast cells grow rapidly. If there's any genetic damage in the breast cells before pregnancy, it's copied as the cells grow. This increased genetic damage in the cells can lead to breast cancer.
The chance of having such genetic damage goes up with age. This may help explain why women who have their first child at a later age have a higher risk of breast cancer than women who have their first child at a younger age.
In general, the more childbirths a woman has had, the lower her risk of breast cancer tends to be [6-11]. After the first child, each childbirth lowers risk.
Some findings show giving birth only lowers the risk of estrogen receptor-positive, with no effect on the risk of estrogen receptor-negative (including triple negative) breast cancers [12-13].
In terms of lowering the risk of breast cancer, women whose childbirths are spaced close together may get more benefit than women whose childbirths are spaced far apart . The exact reasons for this are unclear, but may be related to changes in breast cells that occur during pregnancy.
Women who never give birth have a slightly higher risk of breast cancer compared to women who have had more than one childbirth .
However, women over age 35 who give birth only once have a slightly higher lifetime risk of breast cancer compared to women who never give birth .
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.
Young Women and Breast Cancer
Research Fast Facts: Prevention