Parity, age at first birth, and risk of death from liver cancer: Evidence from a cohort in Taiwan

Background and Aim: The present study was undertaken to examine whether there is an association between parity and age at first birth and risk of liver cancer. Methods: The study cohort consisted of 1 292 462 women who had a first and singleton childbirth between 1 January 1978 and 31 December 1987. We tracked each woman from the time of their first childbirth to 31 December 2007, and their vital status was ascertained by linking records with the computerized mortality database. Cox proportional hazard regression models were used to estimate the relative risks (RR) of death from liver cancer associated with parity and age at first birth. Results: There were 826 liver cancer deaths during 32 464 186.58 person‐years of follow‐up. The mortality rate of liver cancer was 2.54 cases per 100 000 person‐years. The adjusted RR was 1.59 (95% confidence interval [CI] = 1.36–1.86) for women who gave birth between 26 and 30, 2.41 (95% CI = 1.81–3.20) for women who gave birth between 31 and 35, and 6.26 (95% CI = 4.27–9.19) for women who gave birth after 35 years of age, respectively, when compared with women who gave birth at less than 25 years of age. The adjusted RR was 0.72 (95% CI = 0.59–0.87) for women who had two to three children, and 0.63 (95% CI = 0.47–0.84) for women with four or more births, respectively, when compared with women who had given birth to only one child. Conclusions: The present study suggests that reproductive factors (parity and early age at first birth) may confer a protective effect on the risk of liver cancer.