Age at First Childbirth and Number of Childbirths
The link between having children and the risk of breast cancer is complex. It’s related to:
- Your age when you give birth to your first child
- The number of times you give birth
Age at first childbirth
A first pregnancy is linked to an increased short-term risk of breast cancer, but a decreased long-term risk of breast cancer. The impact of these risks depends on a woman’s age at the time of her first pregnancy [6-11].
Women who give birth to their first child at age 35 or younger tend to have a decreased risk of breast cancer [6-10].
Women who give birth to their first child at later ages have a higher risk of breast cancer than women who have their first child at younger ages [6-11].
Women who are over 35 when they give birth to their first child have a small increased risk of breast cancer compared to those who never give birth . For these women, the increased risk related to a first pregnancy is never fully offset by the long-term decreased risk related to childbirth .
Why does age matter?
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.
Number of times you give birth
In general, the more times women have given birth, the lower the risk of breast cancer tends to be [6-10,17]. After the first child, each childbirth is linked to a small, additional decreased risk.
Spacing of births
Among women who have given birth, those whose childbirths were spaced close together may have a lower risk of breast cancer than those whose childbirths were spaced far apart . The reasons for this are unclear but may be related to changes in breast cells that occur during pregnancy.
Never giving birth
Women who never give birth have a slightly higher risk of breast cancer compared to women who’ve had more than one childbirth .
However, women who give birth only once and are older than 35 at the time have a slightly higher risk of breast cancer compared to women who never give birth .