Ovarian cancer
Ovarian cancer is related to the amount of time spent ovulating. Thus not having children is a risk factor for ovarian cancer, likely because ovulation is suppressed via pregnancy. During ovulation, cells are constantly stimulated to divide while ovulatory cycles continue. Therefore, people who have not borne children are at twice the risk of ovarian cancer than those who have. A longer period of ovulation caused by early first menstruation and late menopause is also a risk factor. Both obesity and hormone replacement therapy also raise the risk.