ABSTRACT
The authors claim that there is no satisfactory explanation for the effect of pregnancy on the risk of breast cancer. Breast cancer is commoner among women who have never borne children than among parous women and the longer a woman delays her first pregnancy the more she increases her risk of developing the disease. It has been suggested that prolonged use of oral contraceptives before first full-term pregnancy may increase the risk of breast cancer, although after this pregnancy the risk is probably unaffected by taking the pill.
