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

Breast Cancer Research

Table 2 Invasive breast cancer risk by birthweight and gestation of first-born singleton offspring by menopausal status^a

Risk factor	Pre-menopausal^a			Post-menopausal^a			Breast cancer overall
Risk factor	No. of cases	HR^b	95% CI	No. of cases	HR^b	95% CI	No. of cases	HR^b	95% CI
Birthweight (g)
< 2000	8	2.05	1.01–4.17^c	10	0.91	0.48-1.70	18	1.21	0.76–1.94
2000–2499	11	0.78	0.42–1.43	56	1.10	0.83–1.45	67	1.03	0.80–1.33
2500–2999	62	1.06	0.79–1.42	231	1.13	0.97–1.32	293	1.12	0.97–1.28
3000–3499	162	1.00		514	1.00		676	1.00
3500–3999	141	1.10	0.88–1.38	360	0.98	0.85–1.12	501	1.01	0.90–1.13
4000–4499	35	1.01	0.70–1.46	86	1.01	0.80–1.27	121	1.01	0.83–1.22
≥ 4500	10	1.73	0.91–3.28	20	1.46	0.93–2.28	30	1.53	1.06–2.21^c
Not known	20	1.76	1.11–2.81^c	41	0.98	0.71–1.35	61	1.14	0.88–1.49
p trend^d		0.55			0.50			0.86
p interaction (trend) = 0.39
Gestation (weeks)
26–31	10	2.38	1.26–4.49^e	12	0.95	0.53–1.68	22	1.30	0.85–1.99
32–36	33	1.23	0.85–1.78	117	1.09	0.89–1.33	150	1.10	0.92–1.32
37–39	116	0.92	0.73–1.15	355	1.14	0.99–1.30	471	1.07	0.95–1.21
40–41	200	1.00		481	1.00		681	1.00
≥ 42	70	0.93	0.71–1.22	175	1.06	0.89–1.26	245	1.02	0.88–1.18
Not known	20	0.83	0.53–1.32	178	1.09	0.91–1.30	198	1.04	0.88–1.22
p trend^d		0.03			0.28			0.05
p interaction (trend) = 0.21

HR hazard ratio, CI confidence interval
^aMenopausal status at breast cancer incidence
^bAdjusted 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)
^cp < 0.05
^dExcluding not known category
^ep < 0.01

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