Time since last birth and the risk of ovarian cancer

While parity is a protective factor in ovarian cancer, the role of time factors of pregnancy and birth is still controversial. We considered therefore the role of birth timing in the risk in ovarian cancer from a large case-control study.

Cases were 971 women (age range 22-74 years, median age 54) with histologically confirmed, incident epithelial ovarian cancer, interviewed between 1983 and 1991 in a network of hospitals in Milan, Italy. Controls were 2758 women (age range 23-74 years, median age 52) admitted to the same hospitals where cases were identified for acute, nonneoplastic conditions.

In comparison with nulliparous women, the multivariate odds ratios (OR) were 0.8 for women reporting one or two and 0.6 for those with three or more births. No clear association emerged between time since last birth and ovarian cancer. Compared to women who had last given birth since > or =20 years, a moderately increased risk of ovarian cancer was observed in the first 10 years after last birth, with an OR of 1.7 (95% confidence interval, CI 1.0-2.9). When we considered only multiparous women and included in the multivariate analysis allowance for age at first birth, the OR decreased to 1.2 (95% CI 0.6-2.4). No consistent pattern of trends was observed > or =10 years since last pregnancy.

This study confirms the protective effect of parity on ovarian carcinogenesis, but shows no consistent pattern of risk across time since last birth.