Table 2

Adjusted* odds ratios of breast cancer for women who have had a pregnancy ending in miscarriage compared with women with no pregnancy ending in miscarriage

Subgroup	Number of women	Odds ratio (95% CI)	p Value
*Adjusted for age, parity, and age at delivery of first child. †No information on miscarriages/induced abortions before 1981. ‡Adjusted for age only (as includes nulliparous women). §“Unknown” includes women who have had a miscarriage since 1981 (and no live births since 1981) but whose maternal history sequence before 1981 is unknown.
No miscarriage	11448	1.00
Miscarriage	1161	1.02 (0.88 to 1.18)	0.81
Week of gestation (of earliest miscarriage)
No miscarriage	11448	1.00
<9 weeks	192	1.10 (0.78 to 1.55)	0.61
9–10 weeks	178	0.81 (0.55 to 1.19)	0.29
11–12 weeks	162	0.89 (0.60 to 1.32)	0.55
>12 weeks	205	0.90 (0.63 to 1.27)	0.55
Unknown	424	1.20 (0.96 to 1.51)	0.12
Age at miscarriage
No miscarriage	11448	1.00
12–19 years	17	1.34 (0.43 to 4.18)	0.61
20–24 years	134	0.65 (0.38 to 1.09)	0.10
25–29 years	278	0.96 (0.71 to 1.29)	0.77
30+ years	732	1.10 (0.92 to 1.32)	0.29
Number of miscarriages
0	11448	1.00
1	1031	1.01 (0.86 to 1.18)	0.91
2	110	1.19 (0.76 to 1.87)	0.44
3+	20	0.67 (0.20 to 2.32)	0.53
Time since miscarriage
No miscarriage	11448	1.00
<1 year	51	1.16 (0.6 to 2.23)	0.66
1–4 years	253	1.21 (0.9 to 1.62)	0.22
5–9 years	377	1.05 (0.82 to 1.35)	0.70
10+ years	480	0.89 (0.71 to 1.12)	0.33
Temporal sequence†‡
No miscarriage	11448	1.00
Miscarriage while nulliparous	207	1.08 (0.78 to 1.49)	0.66
Live birth then miscarriage	537	0.79 (0.64 to 0.99)	0.04
Unknown sequence§	417	1.11 (0.88 to 1.39)	0.37