No. of cases | Person-years | Age-adjusted HR (95% CI)* | Multivariate-adjusted HR (95% CI)† | |
---|---|---|---|---|
Oral contraceptive use | ||||
Never | 117 | 2 059 995 | 1.00 | 1.00 |
Past | 255 | 2 802 097 | 1.28 (0.99 to 1.65) | 1.18 (0.91 to 1.52) |
Current | 20 | 168 106 | 1.35 (0.80 to 2.28) | 1.22 (0.74 to 2.07) |
≥5 years | 14 | 125 658 | 1.29 (0.71 to 2.35) | 1.16 (0.64 to 2.12) |
<5 years | 6 | 42 446 | 1.51 (0.64 to 3.58) | 1.40 (0.59 to 3.30) |
ptrend‡ | 0.12 | 0.31 | ||
Oral contraceptive use | ||||
Never | 117 | 2 059 995 | 1.00 | 1.00 |
Ever | 275 | 2 970 201 | 1.29 (1.00 to 1.66) | 1.18 (0.92 to 1.52) |
Parity | ||||
0 | 60 | 561 507 | 1.00 | 1.00 |
1 | 53 | 512 984 | 1.03 (0.71 to 1.49) | 1.01 (0.70 to 1.47) |
2 | 122 | 1 567 093 | 0.86 (0.62 to 1.17) | 0.84 (0.61 to 1.15) |
≥3 | 157 | 2 388 612 | 0.85 (0.62 to 1.17) | 0.85 (0.61 to 1.17) |
ptrend§ | 0.22 | 0.22 | ||
Age at menarche | ||||
≤11 years | 82 | 1 186 266 | 0.84 (0.63 to 1.11) | 0.84 (0.63 to 1.12) |
12 years | 115 | 1 394 138 | 1.00 | 1.00 |
13 years | 116 | 1 480 339 | 0.99 (0.76 to 1.28) | 0.97 (0.75 to 1.26) |
≥14 years | 79 | 969 453 | 1.02 (0.76 to 1.35) | 1.00 (0.75 to 1.34) |
Age at first birth¶ | ||||
<22 years | 38 | 377 093 | 1.06 (0.73 to 1.54) | 1.08 (0.74 to 1.57) |
≥22 and <25 years | 124 | 1 689 995 | 1.00 | 1.00 |
≥25 and <29 years | 102 | 1 537 788 | 0.81 (0.62 to 1.06) | 0.81 (0.62 to 1.05) |
≥29 years | 81 | 917 387 | 0.89 (0.65 to 1.21) | 0.88 (0.65 to 1.20) |
↵* Models adjusted for age (months) and cohort (NHS I, NHS II).
↵† Models adjusted for age (months), cohort (NHS I, NHS II), smoking (never, past, current), body mass index (<20, 20–24.9, 25–29.9, ≥30 kg/m2), oral contraceptive use (never, past, current), parity (nulliparous, parous), age at menarche (≤10, 11, 12, 13, ≥14 years), hormonal replacement therapy (never, past, current) and menopause status (pre-menopause, natural menopause, surgical/radiation menopause) and questionnaire cycle.
↵‡ ptrend was estimated by entering oral contraceptive into the model as a continuous variable excluding reference and current categories.
↵§ ptrend was estimated by entering parity into the model as a continuous variable.
↵¶ Analysis restricted to parous women.