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Delivering bigger babies may lead to increased risk of breast cancer

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A new study finds delivering a baby with a high birth weight can more than double a woman’s risk of breast cancer.

Researchers from the University Texas Medical Branch at Galveston used data from two previous studies involving approximately 24,000 women and found those who delivered babies in the top quintile of weight – 8.25 pounds or more – were more than twice as likely to develop breast cancer  than women who delivered smaller babies.

“Women who give birth to large babies have increased risk of breast cancer independent of other risk factors,” said lead author Dr. Radek Bukowski, professor of obstetrics and gynecology in the Division of Maternal-Fetal Medicine at UT.  “It’s important because if [the finding] stands in further studies, it may have an impact on clinical tests for women and may even improve [doctor’s] predictions.”

Bukowski added that, while the study established a weight cut-off point of 8.25 pounds, the association between an infant’s birth weight and a mother’s breast cancer risk may actually be continuous – in other words, the larger the baby, the larger the risk.

“Although we can’t tell 100 percent, it seems the association is likely continuous,” he said.  “But we don’t know if it’s linear – if each gram or pound increase leads to the same amount of increase in risk.”

According to the researchers, larger infants appear to foster certain levels of hormones during pregnancy that increase a woman’s risk of cancer.  Specifically, this ‘pro-carcinogenic environment’ includes high levels of estrogen, low levels of anti-estrogen and the presence of free insulin-like growth factors, which are associated with the progression of breast cancer.

On average, the women in the study did not develop breast cancer until 38 years after delivering their babies, suggesting the body retains the memory of exposure to these hormones long after the pregnancy ends, Bukowski said.

Further studies need to be done before researchers can make clinical recommendations based on these results, but Bukowski recommended that women who may be concerned by the findings can engage in certain practices to reduce their risks of developing cancer and improve their health overall.

“Staying at a healthy weight, engaging in physical exercise and eating a healthy diet can all decrease risk of breast cancer,” Bukowski said. “…Breastfeeding decreases risk as well.”

The study was published in the journal PLoS One.