| Time since first delivery |
---|
< 15 years | ≥15 years |
---|
No. of cases | HRa | 95% CI | No. of cases | HRa | 95% CI |
---|
Birthweight (g) |
  < 2000 | 2 | 0.87 | 0.21–3.54 | 16 | 1.27 | 0.77–2.09 |
 2000–2499 | 6 | 0.80 | 0.35–1.83 | 61 | 1.06 | 0.82–1.38 |
 2500–2999 | 22 | 0.78 | 0.49–1.26 | 271 | 1.16 | 1.00–1.34b |
 3000–3499 | 79 | 1.00 |  | 597 | 1.00 |  |
 3500–3999 | 62 | 0.95 | 0.68–1.32 | 439 | 1.02 | 0.90–1.15 |
 4000–4499 | 18 | 0.94 | 0.56–1.58 | 103 | 1.01 | 0.82–1.25 |
  ≥ 4500 | 5 | 1.37 | 0.55–3.39 | 25 | 1.56 | 1.04–2.33b |
 Not known | 8 | 1.48 | 0.72–3.07 | 53 | 1.11 | 0.83–1.47 |
 p trendc |  |
0.42
| Â | Â |
0.53
| Â |
p interaction (trend) = 0.32 |
Gestation (weeks) |
 26–31 | 4 | 1.93 | 0.71–5.27 | 18 | 1.21 | 0.75–1.94 |
 32–36 | 17 | 1.30 | 0.78–2.19 | 133 | 1.09 | 0.90–1.32 |
 37–39 | 46 | 0.73 | 0.51–1.04 | 425 | 1.13 | 1.00–1.28 |
 40–41 | 94 | 1.00 |  | 587 | 1.00 |  |
  ≥ 42 | 33 | 0.95 | 0.64–1.42 | 212 | 1.03 | 0.88–1.20 |
 Not known | 8 | 0.84 | 0.41–1.73 | 190 | 1.06 | 0.90–1.25 |
 p trendc |  |
0.32
| Â | Â |
0.09
| Â |
p interaction (trend) = 0.72 |
- HRÂ hazard ratio, CI confidence interval
- aAdjusted for: attained age (Cox regression time scale); time since recruitment to cohort (0, 1–2, 3+ years); birth cohort (1908–1939, 1940–1949, 1950–1959, 1960–1969, 1970–1996); benign breast disease (yes, no); family history of breast cancer in first-degree relatives (yes, no); socio-economic score (ACORN score as trend, missing); own birthweight (trend, missing); age at menarche (trend, missing); parity (trend); age at first pregnancy (trend); cumulative duration of breast feeding (none, duration trend when reported); current oral contraceptive use before menopause (yes, no); height at age 20 (trend, missing); alcohol consumption (never regular, trend current drinker 1 to < 60 g/day, current drinker 60+ g/day, past drinker, drinker with unknown details); age started smoking (never, < 17, 17–19, 20+, missing); physical activity (log(metabolic equivalent) trend, missing); pre-menopausal body mass index at age 20 years (trend, missing); menopausal status (pre- or post-menopausal), and for those post-menopausal, post-menopausal body mass index (trend, missing), menopausal hormone therapy use (never used, ex-user, current oestrogen-only user, current oestrogen plus progestogen user, current user of other types, missing), and age at menopause (trend, missing)
- bp < 0.05
- cExcluding not known category