Table 3.

RRs of breast cancer according to reproductive factors

DeterminantNo. cases/no. in subcohortRR* (95% CI)
Childbirth
    Never141/4301.00
    Ever190/7960.75 (0.60-0.94)
No. births
    1111/3900.86 (0.67-1.11)
    263/3100.65 (0.48-0.88)
    ≥316/960.58 (0.34-1.00)
Per additional birth among parous women0.81 (0.65-1.00)
Age at first birth (y)
    <2557/2450.77 (0.56-1.05)
    25-2943/2320.59 (0.42-0.84)
    ≥3090/3190.85 (0.65-1.11)
Per 5 y among parous women1.02 (0.91-1.16)
Age at last birth (y)
    <3067/2760.80 (0.60-1.08)
    30-3576/3170.74 (0.56-0.99)
    ≥3547/2030.70 (0.50-0.99)
Per 5 y among parous women1.01 (0.90-1.14)
  • NOTE: All analyses were stratified according to calendar year (in categories) and age at start of follow-up (in categories).

  • * All RRs (except childbirth) were adjusted for childbirth (ever/never) and number of additional births (linear).