Table 4.

Associations between number of full-term pregnancies and breast cancer risk, stratified by age at first full-term pregnancy (<25, ≥25 years) and breastfeeding status (ever/never), for all women ages 55 to 64 years in the Women's CARE Study cases

All women
Never breastfed
Ever breastfed
No. full-term pregnancies*n (case/control)OR (95% CI)n (case/control)OR (95% CI)
Age at first full-term pregnancy <25 y
    0140/1071.00140/1071.00
    155/400.97 (0.59-1.59)38/280.92 (0.52-1.62)
    2127/1140.81 (0.56-1.18)120/1130.76 (0.53-1.10)
    ≥3236/2730.62 (0.44-0.86)394/5080.54 (0.40-0.73)
Ptrend0.0020.0001
Pheterogeneity of trend ever vs never breastfed0.68
Age at first full-term pregnancy ≥25 y
    0140/1071.00140/1071.00
    158/550.89 (0.56-1.41)32/241.00 (0.55-1.84)
    267/530.99 (0.63-1.54)75/700.77 (0.49-1.20)
    ≥357/202.19 (1.22-3.96)58/500.80 (0.50-1.29)
Ptrend0.060.24
Pheterogeneity ever vs never breastfed0.04
  • NOTE: Unconditional logistic regression used to calculate OR and 95% CI; models include categories of age, race, study site, education, age at menarche, and family history of breast cancer.

  • * These models used all nulligravida as the reference group.

  • Test for heterogeneity of parity trend effect by breastfeeding status among parous women.