Having children is associated with a decreased risk of endometrial cancer. 

The risk of endometrial cancer is about 25% lower in women who have one child compared with those who have never had children. The risk of endometrial cancer decreases as the number of children that a woman has increases. For example, the risk of endometrial cancer in a woman with three children is about half that of a woman who has not had children. Conversely, not having children is associated with an increased risk of endometrial cancer compared with having children.

The association between having children and decreased risk of endometrial cancer is likely to be due to hormones. Studies suggest that the female hormone oestrogen is associated with risk of endometrial cancer. When a woman is pregnant, her usual menstrual cycle is interrupted. This reduces the length of time her body is exposed to oestrogen and this may lower her risk. Hormone changes during childbirth may also be involved. The physical process of childbirth may also lower the risk of endometrial cancer by removing cancer-causing cells from the endometrium during delivery.