Table 2.

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

	BRCA1 (n = 1,847 pairs)	P	BRCA2 (n = 714 pairs)	P
	OR (95%CI)		OR (95%CI)
Age at menarche (years)1
≤ 11	1.00 (reference)		1.00 (reference)
12	0.66 (0.52–0.84)	0.0005	0.85(0.61–1.20)	0.36
13	0.74 (0.59–0.92)	0.007	0.84(0.60–1.16)	0.28
14	0.65 (0.51–0.84)	0.0002	0.98(0.65–1.46)	0.90
≥ 15	0.58 (0.45–0.74)	<0.0001	1.27(0.82–1.96)	0.28
Trend	0.91 (0.86–0.96)	<0.0001	1.05(0.96–1.15)	0.28
Parity (per birth)2
Nulliparous	1.00 (reference)		1.00 (reference)
1	1.36 (1.03–1.80)	0.03	1.57 (1.03–2.40)	0.04
2	1.39 (1.07–1.82)	0.01	1.46 (1.00–2.14)	0.05
3	1.44 (1.06–1.95)	0.02	1.45 (0.94–2.22)	0.09
≥ 4	1.19 (0.82–1.74)	0.37	0.94 (0.53–1.67)	0.84
Trend	1.07 (0.99–1.15)	0.11	1.04 (0.93–1.16)	0.49
Breastfeeding (years)3
0	1.00 (reference)		1.00 (reference)
≤ 1	0.81 (0.66–1.00)	0.05	1.03 (0.76–1.40)	0.85
1 – ≤ 2	0.65 (0.50–0.85)	0.001	1.04 (0.70–1.53)	0.86
2 – ≤ 3	0.51 (0.35–0.75)	0.0006	1.33 (0.76–2.32)	0.31
> 3	0.45 (0.30–0.68)	0.0002	1.02 (0.56–1.88)	0.94
Trend	0.82 (0.75–0.89)	<0.0001	1.01 (0.95–1.08)	0.68
OC use (years)4
0	1.00 (reference)		1.00 (reference)
≤ 1	1.15 (0.90–1.47)	0.27	1.01 (0.71–1.46)	0.93
1 – ≤ 2	0.89 (0.65–1.22)	0.47	1.15 (0.72–1.84)	0.56
2 – ≤ 3	0.92 (0.66–1.27)	0.60	0.90 (0.55–1.46)	0.66
> 3	1.10 (0.82–1.34)	0.32	1.03 (0.77–1.37)	0.86
Trend	1.02 (0.97–1.07)	0.45	1.04 (0.92–1.17)	0.54

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

¹Estimate adjusted for parity, breastfeeding and oral contraceptive use.

²Estimate adjusted for age at menarche, breastfeeding and oral contraceptive use.

³Estimate adjusted for age at menarche, parity and oral contraceptive use.

⁴Estimate adjusted for age at menarche, breastfeeding and parity.