The results of the study suggest that the current view about childbirth and breast cancer risk should be modified to explain that multiple births at an earlier age decrease a woman's risk of breast cancer. According to Jan Wohlfahrt and Mads Melbye of the Staten Serum Institut in Copenhagen, a woman's breast cancer risk is related to her age at any of her births. Among women who have a first child before age 25, each additional birth reduces their risk of breast cancer. According to the researchers, for every five-year increase in age when she has her first, second, third, or fourth child, a woman's risk of breast cancer increases. Thus Wohlfahrt and Melbye conclude that a woman's early reproductive years could be key and that having children during these years may reduce the long-term risk of breast cancer.
Experts believe that estrogen exposure plays a role in breast cancer risk.
The more menstrual cycles a woman has throughout her lifetime, the higher her risk of breast cancer. During pregnancy, women do not typically experience menstrual cycles, which is thought to reduce the risk of breast cancer. A woman's age when she has children and when she begins and finishes menstruation are only a few risk factors for breast cancer. All women between 20 and 39 years of age should practice monthly breast self-exams and have a physician performed clinical breast exam at least every three years. All women 40 years of age and older should have annual screening mammograms, practice monthly breast self-exams, and have yearly clinical breast exams.