Table 2. Hazard ratios and 95% confidence intervals for the association of reproductive and menstrual factors with colorectal cancer incidence among women enrolled in the WHI-OS.
| Factor | N cases | Age-adjusted HR (95% CI) | Multivariable HRa (95% CI) |
|---|---|---|---|
|
Age at menarche (years) | |||
| ⩽10 | 40 | 1.16 (0.82–1.63) | 1.09 (0.76–1.56) |
| 11–12 | 315 | 1.00 (referent) | 1.00 (referent) |
| 13–14 | 420 | 0.91 (0.78–1.06) | 0.95 (0.81–1.11) |
| ⩾15 | 192 | 0.81 (0.67–0.98) | 0.82 (0.67–1.00) |
| P-trend | 0.08 | 0.2 | |
|
Age at first child's birth (years) | |||
| <20 | 123 | 1.00 (referent) | 1.00 (referent) |
| 20–29 | 664 | 0.88 (0.72–1.08) | 0.98 (0.78–1.23) |
| ⩾30 | 92 | 0.85 (0.64–1.14) | 0.96 (0.70–1.31) |
| P-trend | 0.45 | 0.96 | |
|
Age at last child's birth (years) | |||
| <25 | 112 | 1.00 (referent) | 1.00 (referent) |
| 25–29 | 258 | 0.83 (0.66–1.05) | 0.95 (0.74–1.22) |
| 30–34 | 275 | 0.77 (0.61–0.97) | 0.88 (0.68–1.13) |
| 35–39 | 178 | 0.87 (0.67–1.11) | 0.94 (0.71–1.24) |
| ⩾40 | 49 | 0.89 (0.62–1.26) | 0.91 (0.62–1.34) |
| P-trend | 0.25 | 0.86 | |
|
Pregnancy | |||
| Never | 123 | 1.00 (referent) | 1.00 (referent) |
| Ever | 1025 | 0.88 (0.73–1.07) | 0.82 (0.67–1.00) |
|
Parity | |||
| Nulliparous | 158 | 1.00 (referent) | 1.00 (referent) |
| 1 child only | 100 | 0.89 (0.69–1.15) | 0.86 (0.65–1.13) |
| 2 children | 269 | 0.80 (0.65–0.98) | 0.80 (0.64–0.99) |
| 3 children | 265 | 0.81 (0.66–1.00) | 0.80 (0.65–1.00) |
| ⩾4 children | 351 | 0.90 (0.74–1.09) | 0.85 (0.69–1.04) |
| P-trend | 0.2 | 0.28 | |
|
Induced abortion | |||
| Never | 864 | 1.00 (referent) | 1.00 (referent) |
| Ever | 82 | 1.13 (0.89–1.44) | 1.12 (0.87–1.45) |
|
Breastfed for ⩾1 month | |||
| No | 567 | 1.00 (referent) | 1.00 (referent) |
| Yes | 563 | 0.90 (0.79–1.01) | 0.95 (0.83–1.08) |
|
Age at menopause (years) | |||
| <40 | 132 | 1.00 (referent) | 1.00 (referent) |
| 40–44 | 152 | 0.90 (0.71–1.15) | 0.88 (0.68–1.14) |
| 45–49 | 269 | 0.96 (0.77–1.19) | 0.98 (0.78–1.24) |
| 50–54 | 364 | 0.91 (0.74–1.12) | 0.90 (0.72–1.12) |
| ⩾55 | 135 | 0.94 (0.73–1.21) | 0.98 (0.75–1.28) |
| P-trend | 0.88 | 0.67 | |
|
Hysterectomy | |||
| No | 673 | 1.00 (referent) | 1.00 (referent) |
| Yes | 476 | 0.97 (0.86–1.10) | 1.06 (0.93–1.22) |
|
Bilateral oophorectomy | |||
| No | 886 | 1.00 (referent) | 1.00 (referent) |
| Yes | 233 | 0.97 (0.84–1.13) | 1.09 (0.93–1.28) |
|
Age at oophorectomy (years) | |||
| ⩽34 | 46 | 1.00 (referent) | 1.00 (referent) |
| 35–39 | 57 | 1.48 (1.00–2.20) | 1.51 (0.99–2.31) |
| 40–44 | 67 | 1.20 (0.82–1.77) | 1.28 (0.84–1.94) |
| 45–49 | 65 | 0.93 (0.63–1.38) | 1.07 (0.70–1.63) |
| ⩾50 | 111 | 1.13 (0.80–1.61) | 1.37 (0.94–2.00) |
| P-trend | 0.12 | 0.22 | |
|
Oral contraceptive use | |||
| Never | 839 | 1.00 (referent) | 1.00 (referent) |
| Ever | 310 | 0.72 (0.62–0.83) | 0.74 (0.63–0.86) |
|
Duration of OC use (years) | |||
| 1 | 96 | 1.00 (referent) | 1.00 (referent) |
| 2 | 58 | 1.08 (0.77–1.52) | 1.14 (0.80–1.62) |
| 3 | 83 | 1.19 (0.87–1.61) | 1.18 (0.85–1.63) |
| 4 | 73 | 0.94 (0.68–1.29) | 0.94 (0.67–1.32) |
| P-trend | 0.52 | 0.55 | |
a
Multivariable model adjusted for age, family history of colorectal cancer, race/ethnicity, education level, hormone therapy status, a history of diabetes, smoking status and body mass index.