Table 3 Adjusted hazard ratios and 95% confidence intervals for reproductive factors and gastric cancer risk in 73 442 women from 1997 to 2004 in Shanghai, China.
| Characteristics† | Cohort | Cases | Age‐adjusted | Multivariate‐adjusted* |
|---|---|---|---|---|
| Person‐years (%) | No. (%) | HR (95% CI) | HR (95% CI) | |
| Pregnancies | ||||
| Continuous variable | 1.02 (0.91 to 1.13) | 0.99 (0.89 to 1.11) | ||
| 0 | 11 062 (2.6) | 4 (2.6) | 0.95 (0.31 to 2.87) | 0.95 (0.31 to 2.88) |
| 1 | 67 003 (16.0) | 16 (10.4) | 1.00 (Ref) | 1.00 (Ref) |
| 2 | 122 848 (29.3) | 23 (14.9) | 0.69 (0.36 to 1.30) | 0.69 (0.37 to 1.31) |
| 3 | 101 418 (24.2) | 43 (27.9) | 1.13 (0.62 to 2.04) | 1.11 (0.61 to 2.01) |
| ⩾4 | 116 929 (27.9) | 68 (44.2) | 0.95 (0.52 to 1.73) | 0.88 (0.48 to 1.62) |
| p Value for trend | 0.675 | 0.950 | ||
| Live births | ||||
| Continuous variable | 1.01 (0.88 to 1.17) | 0.96 (0.83 to 1.12) | ||
| 0 | 13 648 (3.3) | 4 (2.6) | 0.73 (0.25 to 2.08) | 0.69 (0.24 to 2.00) |
| 1 | 229 076 (54.6) | 49 (31.8) | 1.00 (Ref) | 1.00 (Ref) |
| 2 | 89 810 (21.4) | 37 (24.0) | 0.78 (0.47 to 1.32) | 0.77 (0.45 to 1.30) |
| 3 | 43 676 (10.4) | 27 (17.5) | 0.82 (0.44 to 1.52) | 0.70 (0.37 to 1.34) |
| ⩾4 | 43 050 (10.3) | 37 (24.0) | 0.91 (0.49 to 1.70) | 0.73 (0.38 to 1.41) |
| p Value for trend | 0.909 | 0.574 | ||
| Age at first birth‡ | ||||
| Continuous variable | 0.96 (0.92 to 1.00) | 0.96 (0.92 to 1.01) | ||
| <24 | 100 383 (24.6) | 63 (42.0) | 1.03 (0.71 to 1.50) | 0.93 (0.63 to 1.39) |
| 24 to 29 | 234 204 (57.4) | 72 (48.0) | 1.00 (Ref) | 1.00 (Ref) |
| >29 | 73 610 (18.0) | 15 (10.0) | 0.75 (0.43 to 1.31) | 0.77 (0.44 to 1.35) |
| p Value for trend | 0.379 | 0.708 | ||
| Total months breast feeding‡ | ||||
| Continuous Variable/10 months | 0.99 (0.97 to 1.02) | 0.99 (0.97 to 1.02) | ||
| <10 | 101 035 (24.8) | 19 (12.7) | 0.78 (0.46 to 1.33) | 0.81 (0.47 to 1.39) |
| 10 to 60 | 206 394 (50.6) | 98 (65.3) | 1.00 (Ref) | 1.00 (Ref) |
| >60 | 100 768 (24.7) | 33 (22.0) | 0.75 (0.50 to 1.12) | 0.75 (0.50 to 1.12) |
| p Value for trend | 0.562 | 0.484 | ||
| Months breast feeding per child‡ | ||||
| Continuous variable (months) | 1.00 (0.99 to 1.00) | 1.00 (0.99 to 1.01) | ||
| <4 | 95 309 (23.3) | 21 (14.0) | 0.85 (0.52 to 1.39) | 0.89 (0.54 to 1.47) |
| 4 to 14 | 212 661 (52.1) | 97 (64.7) | 1.00 (Ref) | 1.00 (Ref) |
| >14 | 100 227 (24.6) | 32 (21.3) | 0.78 (0.52 to 1.17) | 0.79 (0.53 to 1.18) |
| p Value for trend | 0.578 | 0.499 | ||
| IUD use | ||||
| No | 188 853 (45.0) | 90 (58.4) | 1.00 (Ref) | 1.00 (Ref) |
| Yes | 230 407 (55.0) | 64 (41.6) | 1.56 (1.06 to 2.31) | 1.61 (1.08 to 2.39) |
| IUD duration (months) | ||||
| Continuous Variable/5 months | 1.14 (1.02 to 1.27) | 1.14 (1.02 to 1.28) | ||
| Non‐users or used for <1 year | 195 958 (46.7) | 92 (59.7) | 0.60 (0.37 to 0.97) | 0.58 (0.36 to 0.95) |
| 0 to 14 | 77 146 (18.4) | 25 (16.2) | 1.00 (Ref) | 1.00 (Ref) |
| 14 to 20 | 90 429 (21.6) | 16 (10.4) | 0.83 (0.43 to 1.58) | 0.83 (0.44 to 1.59) |
| >20 | 55 720 (13.3) | 21 (13.6) | 1.03 (0.57 to 1.87) | 1.04 (0.57 to 1.90) |
| p Value for trend | 0.044 | 0.032 | ||
| Oral contraceptive use | ||||
| No | 333 571 (79.6) | 121 (78.6) | 1.00 (Ref) | 1.00 (Ref) |
| Yes | 85 688 (20.4) | 33 (21.4) | 1.04 (0.70 to 1.54) | 1.05 (0.70 to 1.56) |
| Received contraceptive shot | ||||
| No | 408 448 (97.4) | 149 (96.8) | 1.00 (Ref) | 1.00 (Ref) |
| Yes | 10 805 (2.6) | 5 (3.3) | 1.36 (0.56 to 3.33) | 1.38 (0.56 to 3.38) |
HR, hazard ratio; IUD, intrauterine device; Ref, reference.
*Adjusted for age, body mass index, education, income, cigarette smoking status (ever, never), and smoking dose (packs/day).
†Categories may not add up to 419 260 person‐years or 154 cases as a result of missing data.
‡Restricted to parous women.