Our large study size allowed examination of associations with several early-life exposures. By using polytomous logistic regression, we could evaluate exposures associated with both early and late menarche. In addition, we could evaluate associations with prenatal exposures that are specific to certain birth cohorts (i.e. DES) or that may have occurred at different rates over time (e.g. smoking). Effects of early-life exposures on age at menarche may be important because early menarche is related to breast cancer and other health conditions in adulthood.2 Historical exposures, such as maternal DES use, continue to be relevant for the majority of women at risk for breast cancer today.
