Objective: A recent analysis suggested that ovarian cancer risk increased with time since last birth, possibly because of some aspect of pregnancy that affects the clearance of cells that have undergone malignant transformation. We analyzed data from four case-control studies pertaining to ovarian cancer risk in relation to age at first pregnancy, age at last pregnancy, and years since last pregnancy: 628 cases and 3432 neighborhood or population controls, ages 18-79, were included.
Methods: We used logistic regression to analyze associations between ovarian cancer risk, controlling for study, age (at diagnosis or corresponding reference age for controls), race, parity, oral contraceptive use, tubal ligation, family history of ovarian or breast cancer, and excluding women with a history of infertility.
Results: An early age at first pregnancy was associated with an increased risk of ovarian cancer (odds ratio 1.4, 95% confidence interval (1.1-1.8) for ages < or =19 compared to > or =25). Years since last pregnancy was also associated with increased ovarian cancer risk, with odds ratios of 1.4, 1.4, 1.8, and 2.1 for 10-14, 15-19, 20-24, and > or =25 years compared to 0-9 years (trend test p = 0.004), respectively.
Conclusion: These observations support the results from the previous study, and raise additional questions about the role of pregnancy in the etiology of ovarian cancer.