Table 2.

Analysis of the potential modifying effects of other risk factors on the relationship of OC use and BrCa risk.

Variables	Studies, N (Ref.)	OR (95% CI)	p	I2 (%)
Taking OC
ever vs. never	42 [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67]	1.15 (1.01, 1.31)	0.0358	92.32
The period of OC using
≤5 years	13 [28,33,37,38,41,48,49,50,51,53,59,62,66]	0.92 (0.77, 1.10)	0.3674	85.86
>5 years		1.05 (0.88, 1.25)	0.5787	82.95
Age of menarche
≤12 years vs. >12 years	29 [26,27,30,32,33,34,35,36,37,38,39,41,43,44,47,48,49,50,51,52,54,55,56,57,58,61,62,64,66]	1.18 (1.07, 1.31)	0.0016	80.71
Parity
Nulliparous vs. Parous	30 [26,27,30,34,35,36,37,38,39,41,42,43,45,47,48,49,50,51,52,54,55,56,57,58,61,62,63,65,66,67]	1.22 (1.04, 1.43)	0.0146	89.88
Age at first pregnancy
≥25 years vs. <25 years	14 [27,35,36,37,39,41,43,49,51,55,62,63,66,67]	1.09 (0.94, 1.25)	0.2599	86.64
≥30 years vs. <30 years	6 [26,48,52,58,64,65]	3.08 (1.10, 8.60)	0.0322	97.49
Breastfeeding
No vs. Yes	27 [26,29,30,32,33,36,37,38,39,41,43,44,45,46,47,48,50,51,52,54,58,61,62,64,65,66,67]	1.36 (1.13, 1.63)	0.0010	91.81
Menopausal status
Post- vs. Pre-	22 [26,32,34,35,36,37,39,42,43,44,45,46,47,48,50,52,54,55,58,62,63,64]	1.36 (1.14, 1.63)	0.0007	92.86
Family history of BrCa
Yes vs. No	29 [27,28,29,30,32,33,34,35,37,39,41,43,44,45,46,48,49,50,51,52,54,55,57,58,61,63,64,66,67]	1.72 (1.32, 2.24)	0.0001	93.07
Body mass index (kg/m2)
≥30 (obesitas) vs. <30	16 [26,27,28,29,32,34,39,41,44,49,51,54,55,57,63,66]	1.19 (0.95, 1.5)	0.1289	90.46
Tobacco smoking
Yes vs. No	14 [26,28,29,30,36,42,49,52,54,58,62,64,66,67]	1.52 (1.26, 1.83)	0.0000	72.32
Diabetes
Yes vs. No	4 [26,29,32,39]	1.99 (0.60, 6.62)	0.2605	93.49