Table 3.

Reproductive factors in relation to ER±/PR± and ER/PR breast cancer by age

 ER+/PR+ER/PR
Age <45Age ≥45Age <45Age ≥45
CasesHR (95% CI)CasesHR (95% CI)CasesHR (95% CI)CasesHR (95% CI)
Number of births
 0311.00 (Reference)791.00 (Reference)291.00 (Reference)271.00 (Reference)
 1360.90 (0.47–1.71)760.68 (0.48–0.98)220.81 (0.41–1.59)421.17 (0.69–1.96)
 2250.71 (0.37–1.39)1110.73 (0.53–1.01)311.37 (0.74–2.56)761.61 (1.01–2.57)
 ≥3140.76 (0.36–1.59)850.47 (0.33–0.66)231.89 (1.00–3.59)661.39 (0.86–2.25)
Ptrend = 0.32Ptrend < 0.0001Ptrend = 0.02Ptrend = 0.11
Age at first birth
 <20161.00 (Reference)871.00 (Reference)171.00 (Reference)651.00 (Reference)
 20–24130.69 (0.33–1.46)930.93 (0.69–1.26)191.13 (0.52–1.99)630.93 (0.65–1.33)
 25–29201.23 (0.61–2.49)601.22 (0.86–1.73)211.66 (0.61–2.59)381.21 (0.79–1.86)
 ≥30261.75 (0.85–3.61)321.14 (0.73–1.79)192.24 (0.76–3.86)181.16 (0.65–2.07)
Ptrend = 0.04Ptrend = 0.31Ptrend = 0.03Ptrend = 0.42
Years since last birth
 ≥15201.00 (Reference)2441.00 (Reference)141.00 (Reference)1701.00 (Reference)
 10–14110.71 (0.33–1.51)151.15 (0.65–2.03)201.84 (0.90–3.74)91.01 (0.49–2.05)
 <10431.61 (0.88–2.95)81.51 (0.71–3.23)422.18 (1.08–4.41)20.66 (0.16–2.79)
Ptrend = 0.08Ptrend = 0.23Ptrend = 0.03Ptrend = 0.66
Ever breastfed
 No321.00 (Reference)1601.00 (Reference)401.00 (Reference)1221.00 (Reference)
 Yes431.30 (0.80–2.12)1081.10 (0.85–1.42)360.78 (0.48–1.26)590.79 (0.57–1.09)

NOTE: HRs were derived from models that adjusted for age, time, geographic region, age at menarche, age at menopause, use of menopausal hormone supplements, use of oral contraceptives, body mass index, physical activity, alcohol intake, cigarette smoking, family history of breast cancer, and each of the other reproductive factors.