Table 3.

Parity and breast cancer risk stratified by hormone receptor expression

First author (reference)Country (study)Cases (n)Births (n)*Risk estimate (95% CI)
ER+ER−
Wohlfahrt (22)Denmark (DBCG)6,0441+0.8 (0.7-0.8)0.9 (0.8-1.0)
Hildreth (42)United States1481+0.6 (0.3-1.1)2.5 (0.8-10.0)
Cooper (36)Australia38011.4 (0.7-2.7)1.3 (0.5-3.4)
20.8 (0.5-1.4)0.8 (0.4-1.9)
3+0.8 (0.5-1.4)1.0 (0.4-2.3)
Hislop (37)Canada (BC)5121-20.8 (0.6-1.0)0.9 (0.6-1.4)
3+0.7 (0.6-1.0)1.3 (0.9-2.0)
McTiernan (39)United States (CASH-WA)2401-20.81.9
3+0.6 (0.3-1.5)1.4 (0.6-3.6)
Stanford (38)United States (CASH-GA)4581-21.0 (0.6-1.6)0.9 (0.6-1.5)
3-40.7 (0.4-1.2)0.8 (0.5-1.3)
5+0.5 (0.2-1.0)1.0 (0.5-1.9)
Kreiger (35)Canada (ON)5281-30.7 (0.5-0.9)0.9 (0.5-1.6)
4+0.7 (0.4-1.1)1.4 (0.6-3.0)
Yoo (41)Japan455Per 1 child1.0 (0.8-1.1)0.9 (0.8-1.2)
PR+PR−
Kreiger (35)Canada (ON)5281-30.6 (0.4-0.9)0.9 (0.6-1.5)
4+0.5 (0.3-0.8)1.6 (0.9-3.1)
Yoo (41)Japan455Per 1 child0.9 (0.7-1.1)1.0 (0.9-1.2)
ER+/PR+ER−/PR−
McCredie (23)Melbourne (Australia)61811.1 (0.7-1.7)1.3 (0.8-2.3)
21.0 (0.7-1.5)1.0 (0.6-1.7)
3+1.0 (0.5-1.2)0.8 (0.4-1.3)
Cotterchio (24)Canada (ON)3,276Premenopause
10.6 (0.4-1.1)1.0 (0.5-2.0)
20.7 (0.4-1.0)1.1 (0.6-2.0)
3+0.4 (0.3-0.8)0.9 (0.5-1.8)
Postmenopause
11.0 (0.7-1.4)0.9 (0.6-1.6)
20.8 (0.6-1.2)0.7 (0.5-1.2)
3+0.7 (0.5-1.0)0.7 (0.5-1.1)
Britton (29)United States (WISH)1,2121+0.8 (0.6-1.1)0.8 (0.5-1.2)
Potter (17)United States (IWHS)6101-20.8 (0.5-1.1)2.1 (0.6-6.9)
3+0.8 (0.5-1.1)2.2 (0.7-7.2)
Yoo (41)Japan455Per 1 child1.0 (0.8-1.2)1.0 (0.8-1.2)
  • NOTE: Adjustment for other reproductive variables was sometimes unclear. Hildreth et al., McTiernan et al., and Yoo et al. adjusted for age at first birth and breast-feeding, assigning nulliparous women a value of zero in the model.

  • * Reference group is nulliparous women.

  • ORs were the reported risk estimates for case-control studies and RRs for cohort designs.

  • Age-adjusted only.