Table 3.

Relationship between reproductive factors and risk of breast cancer subtypesa

Luminal ALuminal BTriple-negativeHER2-overexpressing
n (%)n (%)OR (95% CI)n (%)OR (95% CI)n (%)OR (95% CI)
Number of full-term pregnancies
 Nulliparous191 (24.7)39 (30.0)1.00 (ref)291 (22.6)1.00 (ref)92 (19.0)1.00 (ref)
 Parous583 (75.3)91 (70.0)0.82 (0.54–1.24)994 (77.4)1.13 (0.91–1.39)392 (81.0)1.43 (1.08–1.89)b
 1124 (16.0)26 (20.0)1.05 (0.61–1.82)234 (18.2)1.24 (0.93–1.65)83 (17.1)1.43 (0.98–2.08)
 2287 (37.1)40 (30.8)0.73 (0.45–1.18)432 (33.6)1.00 (0.79–1.27)178 (36.8)1.31 (0.96–1.79)
 ≥3172 (22.2)25 (19.2)0.79 (0.46–1.37)328 (25.5)1.27 (0.98–1.66)131 (27.1)1.63 (1.16–2.29)b
 Ptrend (among parous women only)0.4160.7290.431
Age at first full-term pregnancyc
 <2076 (14.0)14 (16.9)1.00 (ref)183 (20.1)1.00 (ref)61 (17.4)1.00 (ref)
 20–24176 (32.4)19 (22.9)0.56 (0.27–1.19)301 (33.1)0.70 (0.51–0.97)b115 (32.8)0.83 (0.55–1.25)
 25–29153 (28.1)25 (30.1)0.82 (0.40–1.69)230 (25.3)0.61 (0.43–0.86)b86 (24.5)0.70 (0.46–1.08)
 30+139 (25.6)25 (30.1)0.84 (0.40–1.73)196 (21.5)0.56 (0.40–0.80)b89 (25.4)0.81 (0.52–1.25)
 Continuous (1-year)1.01 (0.97–1.05)0.97 (0.95–0.99)b0.99 (0.97–1.01)
 Ptrend0.5740.0030.557
Age at menopaused
 <4535 (10.0)9 (21.4)1.00 (ref)136 (23.3)1.00 (ref)43 (18.4)1.00 (ref)
 45–54277 (78.9)29 (69.0)0.41 (0.17–0.97)b396 (67.8)0.41 (0.27–0.63)b166 (70.9)0.50 (0.30–0.83)b
 55+39 (11.1)4 (9.5)0.51 (0.14–1.89)52 (8.9)0.39 (0.22–0.70)b25 (10.7)0.66 (0.33–1.34)
 Continuous (1-year)0.97 (0.91–1.04)0.97 (0.94–1.00)b0.99 (0.96–1.03)
 Ptrend0. 3970.0240.759
  • aNumber in columns may not add up to the total number of cases due to missingness in these variables. ORs were adjusted for reference year, age at reference date, and study site.

  • bStatistically significant at P < 0.05.

  • cRestricted to women who ever had a full-term pregnancy.

  • dRestricted to postmenopausal women with known age at menopause.