Parity and bladder cancer risk: a dose-response meta-analysis

Background: Multiple studies have reported evidence of an inverse association between parity and bladder cancer risk. However, a comprehensive and quantitative assessment of this association has never been conducted. We conducted this study to clarify this issue. Methods: Systematic search of PubMed and Embase was performed to identify all the studies. Studies were selected based on strict screening with inclusion and exclusion criteria. Summary relative risks (RR) with 95% confidence intervals (CI) were calculated by using a fixed-effect model, and the generalized least squares trend estimation was employed to compute study-specific RR and 95% CI per live birth increase. Heterogeneity and publication bias were also evaluated. Results: Twelve studies (6,214 cases and 2,693,350 non-cases) were eligible in this meta-analysis. The pooled RR of bladder cancer for parous versus nulliparous women was 0.76 (95% CI: 0.70-0.82). Results were similar in the studies that adjusted for BMI(RR = 0.66; 95% CI: 0.53-0.81), cigarette smoking (RR = 0.67; 95% CI: 0.57-0.79), and age (RR = 0.77; 95% CI: 0.71-0.84). The dose-response meta-analysis showed a lower bladder cancer risk (RR = 0.95; 95% CI: 0.92-0.98) for each live birth increase in parous women. No evidence of publication bias or significant heterogeneity was detected in the above-mentioned analyses. Conclusions: The finding from current meta-analysis suggest that parity may be related to decreased risk of bladder cancer.