Table 2.

Relationship between various reproductive factors and risk of breast cancer among BRCA1 and BRCA2 mutation carriers

BRCA1 (n = 1,847 pairs); OR (95% CI)PBRCA2 (n = 714 pairs); OR (95%CI)P
Age at menarche,a y
 ≤111.00 (reference)1.00 (reference)
 120.66 (0.52–0.84)0.00050.85 (0.61–1.20)0.36
 130.74 (0.59–0.92)0.0070.84 (0.60–1.16)0.28
 140.65 (0.51–0.84)0.00020.98 (0.65–1.46)0.90
 ≥150.58 (0.45–0.74)<0.00011.27 (0.82–1.96)0.28
 Trend0.91 (0.86–0.96)<0.00011.05 (0.96–1.15)0.28
Parity (per birth)b
 Nulliparous1.00 (reference)1.00 (reference)
 11.36 (1.03–1.80)0.031.57 (1.03–2.40)0.04
 21.39 (1.07–1.82)0.011.46 (1.00–2.14)0.05
 31.44 (1.06–1.95)0.021.45 (0.94–2.22)0.09
 ≥41.19 (0.82–1.74)0.370.94 (0.53–1.67)0.84
 Trend1.07 (0.99–1.15)0.111.04 (0.93–1.16)0.49
Breastfeeding,c y
 01.00 (reference)1.00 (reference)
 ≤ 10.81 (0.66–1.00)0.051.03 (0.76–1.40)0.85
 1–≤20.65 (0.50–0.85)0.0011.04 (0.70–1.53)0.86
 2–≤30.51 (0.35–0.75)0.00061.33 (0.76–2.32)0.31
 >30.45 (0.30–0.68)0.00021.02 (0.56–1.88)0.94
 Trend0.82 (0.75–0.89)<0.00011.01 (0.95–1.08)0.68
Oral contraceptive use,d y
 01.00 (reference)1.00 (reference)
 ≤11.15 (0.90–1.47)0.271.01 (0.71–1.46)0.93
 1–≤20.89 (0.65–1.22)0.471.15 (0.72–1.84)0.56
 2–≤30.92 (0.66–1.27)0.600.90 (0.55–1.46)0.66
 >31.10 (0.82–1.34)0.321.03 (0.77–1.37)0.86
 Trend1.02 (0.97–1.07)0.451.04 (0.92–1.17)0.54

NOTE: Only includes women who had no missing data for age at menarche (n = 2,561).

  • aEstimate adjusted for parity, breastfeeding, and oral contraceptive use.

  • bEstimate adjusted for age at menarche, breastfeeding, and oral contraceptive use.

  • cEstimate adjusted for age at menarche, parity, and oral contraceptive use.

  • dEstimate adjusted for age at menarche, breastfeeding, and parity.