Table 1.

Characteristics of 365 premenopausal women recruited during annual screening mammography at the Joanne Knight Breast Health Center, Washington University School of Medicine

Body size at age 10
1–23–456+
nMean ± SD/percentagenMean ± SD/percentagenMean ± SD/percentagenMean ± SD/percentagePtrenda
Attained age (years)15847.54 ± 4.8312946.72 ± 4.435146.83 ± 4.712745.50 ± 6.150.038
Menarche (years)15813.02 ± 1.5612912.71 ± 2.865112.43 ± 1.632712.78 ± 1.580.144
Age at first birth (years)13826.09 ± 6.129826.35 ± 5.773826.03 ± 6.721924.84 ± 6.240.598
Birth indexb (years)15836.61 ± 25.1212928.66 ± 23.795126.78 ± 24.902731.54 ± 32.660.023
Parity0.008
 Nulliparous2012.66%3124.03%1325.49%829.63%
 One2415.19%2519.38%1325.49%414.81%
 Two6843.04%4333.33%1529.41%622.22%
 Three or more4629.11%3023.26%1019.61%933.33%
Ever breastfed10063.29%7356.59%2854.90%1348.15%0.085
Ever used oral contraceptives14891.77%11387.60%4588.24%2277.78%0.049
Family history of breast cancer3320.89%3023.26%1325.49%1037.04%0.095
Race0.265
 Non-Hispanic White10968.99%8767.44%2956.86%1866.67%
 Black or African American4427.85%3325.58%1733.33%933.33%
 Others53.16%96.98%59.8%00
Education level0.359
 High school or less than high school159.49%107.75%611.76%311.11%
 Post high school training or some college3119.62%2317.83%1019.61%1037.04%
 College graduate6742.41%4635.66%1631.37%1037.04%
 Postgraduate4427.85%5038.76%1937.25%414.81%
Adiposity measures
 Attained height (cm)158164.62 ± 6.79129164.03 ± 7.0951164.25 ± 9.0427166.47 ± 5.520.556
 Attained weight (kg)15877.72 ± 19.5112981.51 ± 21.425192.68 ± 23.822798.33 ± 15.21<0.001
 Attained BMI (kg/m2)15828.69 ± 7.1012930.29 ± 7.845134.49 ± 9.062735.45 ± 5.00<0.001
  • aLinear trends for continuous variables and heterogeneity for categorical variables were tested across body size groups using linear regression model and χ2 test, respectively.

  • bBirth index (years) = attained age minus age at each given birth (the birth index is 0 for nulliparous women).