Characteristic 1 1.5-2 2.5-3 3.5-4 4.5+ Age (years) 42.5 41.8 42.0 42.3 42.5 Birth weight 10.0 11.5 13.9 16.2 18.7 >=3.9 kg, % Age at menarche 12.8 12.6 12.3 12.1 12.0 Total physical 56.3 54.5 51.9 48.4 46.0 activity at ages 12-17 (MET- hr/wk) Age at first birth 26.3 26.5 26.5 26.5 26.5 (years) (among parous women) Family history 9.6 9.7 9.3 9.3 9.5 of breast cancer, %