Table 2.

Associations between parity status and breast cancer stratified by age at first full-term pregnancy (<25 or ≥25 years) among all women ages 55 to 64 years in the Women’s CARE Study and by ERPR status

Parity statusAll women
ERPR positive
ERPR negative
Age at first <25 y
Age at first ≥25 y
Age at first <25 y
Age at first ≥25 y
Age at first <25 y
Age at first ≥25 y
n (case/control)OR (95% CI)n (case/control)OR (95% CI)n (cases)OR (95% CI)n (cases)OR (95% CI)n (cases)OR (95% CI)n (cases)OR (95% CI)
Nulliparous*140/1071.00140/1071.00721.00721.00111.00111.00
≥1 full-term pregnancy970/10760.64 (0.48-0.84)347/2720.97 (0.71-1.31)4430.59 (0.42-0.82)1931.05 (0.73-1.51)1971.62 (0.84-3.11)532.07 (1.03-4.16)
Pheterogeneity ERPR-positive vs ERPR-negative0.0040.06
Pheterogeneity <25 vs ≥25 y0.000070.000010.23
No. full-term pregnancy
    193/681.0090/791.00411.00451.00111.00141.00
    2247/2270.84 (0.58-1.22)142/1230.88 (0.58.1.33)1320.93 (0.59-1.47)831.04 (0.64-1.69)481.61 (0.78-3.31)210.93 (0.43-2.01)
    3246/2920.63 (0.44-0.91)83/531.35 (0.77-2.04)1090.56 (0.35-0.88)481.36 (0.77-2.41)581.50 (0.74-3.04)101.09 (0.43-2.73)
    ≥4384/4890.57 (0.40-0.81)32/171.56 (0.78-3.15)1610.51 (0.33-0.80)171.63 (0.73-3.63)801.10 (0.55-2.19)82.76 (0.94-8.07)
Ptrend0.00010.130.00010.150.260.13
Pheterogeneity ERPR-positive vs ERPR-negative0.060.75
Pheterogeneity <25 vs ≥25 y0.0010.0020.04
  • NOTE: All unconditional logistic regression models include categories of age, race, study site, education, age at menarche, and first-degree family history of breast cancer.

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

  • In addition to factors listed in (1), models include categories of age at first full-term pregnancy.