Compared with women who have never given birth, those who recently had babies may have a slight increased risk of breast cancer that peaks after about five years and then gradually declines, according to a study published this week.
The degree of risk increases with the mother’s age at the time she gave birth.
The results sound disturbing, especially for women who already have more than enough stress taking care of young children. But even with the increase, the risk of breast cancer in young women before menopause remains very low, researchers say.
“We don’t want women to feel alarmed or frightened,” Hazel Nichols, an epidemiologist at the University of North Carolina Lineberger Comprehensive Cancer Center, and lead author of the study, said in an interview.
The results, based on pooled data from 15 studies involving 890,000 women, were published in Annals of Internal Medicine.
To show the risk is small, Nichols explained that in women between ages 41 and 50 who had given birth in the previous three to seven years, the study found that 2.2 percent developed breast cancer, while in those who had not had babies, the figure was 1.9 percent. The increase in risk lasted for about 20 years. No rise in risk was detected in women who had babies before age 25.
But having children also seems to make it less likely that breast cancer will develop later in life, when the disease becomes more common, said Dr. Katrina Armstrong, physician-in-chief at Massachusetts General Hospital and an expert on cancer prevention.