Parity, Age at First Birth, and Risk of Death from Bladder Cancer: A Population-Based Cohort Study in Taiwan

The evidence is limited on the relationship between reproductive factors and bladder cancer (BC). We studied 1,292,462 women who had a first and singleton delivery between 1 January 1978 and 31 December 1987. Each woman in the study cohort was tracked from their first childbirth to 31 December 2009. Vital status of the women was determined by crosswalking records with a computerized mortality database. We used Cox proportional hazard regression models to estimate the hazard ratios (HRs) of death from BC associated with maternal age at first birth and parity. The data showed 63 BC deaths during 34,980,246 person-years of follow-up. BC mortality rate was 0.90 cases for every 100,000 person-years. Compared with women who gave birth under the age of 23, the adjusted HR was 1.24 (95% confidence interval (CI) = 0.66-2.35) for women who gave birth between age 23 and 26 and 2.30 (95% CI = 1.21-4.39) for women who gave birth over the age of 26. Increasing age at first birth (p for trend = 0.01) is associated with a trend in increasing risk of BC mortality. Relative to women who had a single childbirth, the adjusted HRs were 1.17 (95% CI = 0.51-2.69) for women who gave birth to two children, and 1.31 (95% CI = 0.56-3.10) for women with three or more childbirths, respectively. These results were not statistically significant. Study results suggests that giving birth at an early age may confer a protective effect on the risk of death from BC.