A large study found a relationship between birth size and the risk of breast cancer later in life. The larger a baby girl, the higher her risk of breast cancer as an adult.
- greater birth weight
- longer body length
- larger head circumference
all were associated with a higher-than-average risk of breast cancer.
Birth size's effect on breast cancer risk is about the same as some other risk factors:
- age at first period
- age at menopause
- being obese after menopause
The researchers found that:
- For each pound (about half a kilogram) a baby girl's birth weight is above average, her future breast cancer risk goes up by 6%. Average birth weight is about 6.5 pounds (about 3 kilograms).
- Baby girls with the longest birth lengths (more than 20 inches/51 centimeters) were 17% more likely to develop breast cancer as adults than babies who had an average birth length. For each 3/4 of an inch (2 centimeters) a girl's birth length is above average, future breast cancer risk goes up by 6%. Average birth length is about 19 inches (49 centimeters).
- Baby girls with the largest head circumferences (larger than 16 inches/36 centimeters) were 11% more likely to develop breast cancer as adults than babies with average head circumference. For each 3 inches (1.5 centimeters) a baby's head circumference is larger than average, future breast cancer risk increases by 9%. Average head circumference is 13 inches (33 centimeters).
Because this study is so large, it's likely that there is a relationship between birth size and breast cancer risk. While it doesn't offer any new information on how to reduce breast cancer risk, it may help doctors identify women at higher risk so these women can be screened more often.
Still, your birth size isn't something that you can control. But there are many risk factors for breast cancer that you CAN control. Visit the Breastcancer.org Lower Your Risk section to learn about diet and lifestyle choices you can make to keep your risk of breast cancer as low as it can be.