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Table 1 Age-adjusteda percent distribution of baseline characteristics

From: Pregnancy-related factors and the risk of breast carcinoma in situand invasive breast cancer among postmenopausal women in the California Teachers Study cohort

  Total Ever pregnant, % Parous women (number of full-term pregnancy/age at first full-term pregnancy, yrs), %
   No Yes < 3/< 25 < 3/≥ 25 ≥ 3/< 25 ≥ 3/≥ 25
   (n = 8,937) (n = 43,527) (n = 8,034) (n = 14,825) (n = 10,851) (n = 7,372)
Race        
   White 46,624 16.8 83.2 19.8 34.4 28.2 17.7
   African-American 1,622 11.1 88.9 25.9 34.6 28.3 11.2
   Others 4,218 17.2 82.8 17.7 36.0 27.9 18.4
First-degree family history of breast cancer        
   No 43,489 16.6 83.4 19.8 34.5 28.3 17.3
   Yes 7,132 16.8 83.2 19.2 34.5 27.0 19.3
   Unknown 1,843 17.8 82.2 20.8 35.7 27.7 15.9
Age at menarche, years        
   < 13 26,220 16.9 83.1 20.6 34.3 28.7 16.4
   ≥ 13 26,244 16.4 83.6 19.0 34.8 27.6 18.7
BMI, kg/m2        
   < 25 27,583 16.9 83.1 20.4 35.8 26.6 17.2
   25 to 29.9 14,354 15.8 84.2 19.1 32.6 30.0 18.3
   ≥ 30 7,783 17.5 82.5 19.1 33.4 30.6 16.9
   Unknown 2,744 16.0 84.0 18.7 35.6 26.7 19.0
Menopausal HT use        
   Never 10,945 20.4 79.6 16.0 35.5 27.3 21.2
   E only 15,676 15.6 84.4 21.8 31.2 30.4 16.7
   E plus P only 14,959 15.8 84.2 19.8 37.7 25.8 16.7
   Mixed use 7,169 15.7 84.3 21.1 32.7 30.3 15.9
   Unknown type of HT 3,715 15.2 84.8 19.8 35.7 26.7 17.8
Duration of breastfeeding for parous women, months        
   Never 12,628 - - 25.0 39.7 22.0 13.3
   < 6 11,202    24.1 35.2 26.8 13.9
   6 to 11 7,124    19.5 38.2 26.9 15.4
   12 to 23 6,486    11.1 28.4 35.3 25.2
   ≥ 24 3,642    3.3 17.2 44.2 35.3
  1. Results are for 52,464 postmenopausal women in the California Teachers Study followed between 1995 and 2007.aAge distribution in each category of the baseline characteristic variables was adjusted according to age distribution of the 52,464 participants. Abbreviations: BMI, body mass index; HT, hormone therapy; E, estrogen; P, progestin.