Table 3. Summary risk estimates of the association between the number of parity and colorectal cancer risk, highest vs. lowest parity number.
| No. of studies | Summary RR (95% CIs) | Q Statistic | I 2 Value (%) | P h * | P h ** | |
| All studies | 11 | 1.02 (0.89–1.17) | 17.48 | 37.1 | 0.094 | – |
| Subgroup analyses | 0.611 | |||||
| High quality studies (scores ≥8) | 7 | 1.05 (0.94–1.17) | 8.78 | 31.6 | 0.186 | |
| Low quality studies (scores <8) | 4 | 0.97 (0.72–1.31) | 8.08 | 50.5 | 0.089 | |
| Duration of follow-up | 0.641 | |||||
| <10 y | 5 | 1.06 (0.84–1.34) | 8.43 | 52.6 | 0.077 | |
| ≥10 y | 6 | 0.99 (0.85–1.14) | 8.54 | 29.7 | 0.201 | |
| Number of cases | 0.847 | |||||
| <500 | 5 | 1.00 (0.79–1.26) | 6.82 | 41.4 | 0.145 | |
| ≥500 | 6 | 1.03 (0.93–1.15) | 10.59 | 43.4 | 0.102 | |
| Geographic location | 0.339 | |||||
| America | 7 | 1.08 (0.88–1.34) | 11.65 | 48.5 | 0.070 | |
| Europe | 2 | 1.06 (0.90–1.23) | 4.23 | 52.7 | 0.121 | |
| Asia | 2 | 0.85 (0.61–1.17) | 0.04 | 0 | 0.833 | |
| Anatomic cancer site | 0.977 | |||||
| Colon | 8 | 1.04 (0.87–1.24) | 10.67 | 34.4 | 0.154 | |
| Rectum | 6 | 1.04 (0.81–1.35) | 4.57 | 0 | 0.470 | |
| Cancer subsite of colon | 0.881 | |||||
| Proximal colon | 4 | 0.98 (0.70–1.36) | 5.02 | 40.3 | 0.170 | |
| Distal colon | 4 | 0.90 (0.64–1.27) | 2.99 | 0 | 0.393 | |
| Adjustment for confounders or important risk factors | ||||||
| Body mass index | 0.611 | |||||
| Yes | 7 | 1.05 (0.94–1.17) | 8.78 | 31.6 | 0.186 | |
| No | 4 | 0.97 (0.72–1.31) | 8.08 | 50.5 | 0.089 | |
| Diabetes mellitus | 0.787 | |||||
| Yes | 2 | 1.05 (0.92–1.20) | 2.38 | 58.0 | 0.123 | |
| No | 9 | 1.01 (0.84–1.21) | 14.87 | 39.5 | 0.095 | |
| Physical activity | 0.886 | |||||
| Yes | 6 | 1.04 (0.93–1.16) | 8.36 | 40.2 | 0.138 | |
| No | 5 | 1.00 (0.84–1.20) | 9.02 | 44.6 | 0.108 | |
| Cigarette smoking | 0.611 | |||||
| Yes | 7 | 1.05 (0.94–1.17) | 8.78 | 31.6 | 0.186 | |
| No | 4 | 0.97 (0.72–1.31) | 8.08 | 50.5 | 0.089 | |
| Alcohol drinking | 0.886 | |||||
| Yes | 6 | 1.04 (0.93–1.16) | 8.36 | 40.2 | 0.138 | |
| No | 5 | 1.00 (0.84–1.20) | 9.02 | 44.6 | 0.108 | |
| HRT use | 0.616 | |||||
| Yes | 4 | 1.03 (0.89–1.19) | 5.68 | 47.2 | 0.128 | |
| No | 7 | 1.03 (0.90–1.17) | 11.80 | 40.7 | 0.107 | |
| Family history of colorectal cancer/adenomatous polyposis | 0.631 | |||||
| Yes | 5 | 0.95 (0.84–1.07) | 5.97 | 33.0 | 0.201 | |
| No | 6 | 0.95 (0.87–1.03) | 10.38 | 42.2 | 0.110 | |
RR: relative risk; CI: confidence interval; HRT: hormone replacement therapy.
*
P value for heterogeneity within each subgroup.
**
P value for heterogeneity between subgroups with meta-regression analysis.