One study included 410 women in the Framingham Offspring Birth History Study. During the follow-up period, from 1991-2008, 31 women (7.6%) had been diagnosed with breast cancer.
Women with bigger babies had a higher risk of developing breast cancer. That link held true even when scientists considered commonly known risk factors such as BMI, use of hormone replacement therapy, family history and age.
Another tantalizing clue for study authors came from a study of 23,824 mothers of singleton infants participating in the FASTER clinical trial between 1999-2003.
Turns out, women who delivered large babies (8.25 pounds or larger) also had what Bukowski calls a "pro-carcinogenic" hormonal profile.