For women who gave birth at 25: The risk of developing breast cancer within five years was 18 percent higher than that of nonchildbearing peers. (In technical terms, the odds ratio for these women was 1.18.)

For women who gave birth at 30: The risk of developing the disease within five years was 24 percent greater than that of childless peers. (The odds ratio was 1.24.)

And, for women who gave birth at 35: The risk was 26 percent greater than that of peers. (The odds ratio was 1.26.)

These numbers aren't as scary as they sound, however, since the base-line probability of getting cancer at these ages is still low.