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Table 4 Invasive breast cancer risk by birthweight and gestation of firstborn singleton offspring by duration post-delivery

From: Maternal breast cancer risk in relation to birthweight and gestation of her offspring

 

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

  

0.53

 

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

  

0.09

 

p interaction (trend) = 0.72

  1. HR hazard ratio, CI confidence interval
  2. 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)
  3. bp < 0.05
  4. cExcluding not known category