Time since last birth and the risk of ovarian cancer

Objectives. While parity is a protective factor in ovarian cancer, the role of time factors of pregnancy and birth is still controversial. We consider ed therefore the role of birth timing in the risk in ovarian cancer from a large case-control study. Methods. Cases were 971 women (age range 22-74 years, median age 54) with h istologically confirmed, incident epithelial ovarian cancer, interviewed be tween 1983 and 1991 in a network of hospitals in Milan, Italy. Controls wer e 2758 women (age range 23-74 years, median age 52) admitted to the same ho spitals where cases were identified for acute, nonneoplastic conditions. Results, 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 greate r than or equal to 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 wome n and included in the multivariate analysis allowance for age at first birt h, the OR decreased to 1.2 (95% CI 0.6-2.4), No consistent pattern of trend s was observed greater than or equal to 10 years since last pregnancy. Conclusions. This study confirms the protective effect of parity on ovarian carcinogenesis, but shows no consistent pattern of risk across time since last birth. (C) 2001 Academic Press.