Objective: A single live birth compared to nulliparity significantly reduces the risk for ovarian cancer, but exactly how pregnancy reduces ovarian cancer risk is unknown. We sought to determine whether offspring gender, which differentially alters maternal hormonal milieu, may be associated with maternal ovarian cancer risk.
Methods: Parous women (n = 511) with incident ovarian cancer were compared to parous community controls (n = 1136) participating in a population-based case-control study of ovarian cancer (Delaware Valley, 1994-1998). In subgroup specific models for women with one, two, or three births, multivariate logistic regression was used to assess the relationship between ovarian cancer and offspring gender, adjusting for age, race, education, oral contraceptives, breast feeding, tubal ligation, and ovarian cancer family history.
Results: Compared to having all girls, women with all boys tended to have a reduced risk of ovarian cancer (OR = 0.80 95% CI: 0.58, 1.10), while women with boys and girls conferred the greatest protection (OR = 0.58, 95% CI: 0.43, 0.79). Among women with two births, the association was observed for those with one boy and one girl (OR = 0.63, 95% CI: 0.40, 1.00), but not for those with two male offspring (OR = 1.12, 95% CI: 0.68, 1.85). This result was consistent among women with three births (OR = 0.42, 95% CI: 0.21, 0.84; OR = 0.47, 95% CI: 0.23, 0.95; OR = 0.49, 95% CI: 0.20, 1.21; for one, two, and three boys, respectively, compared to all girls).
Conclusion: Compared to having all girls, bearing both male and female offspring may be associated with a decrease in maternal ovarian cancer risk, although the biologic relevance of this observation is unclear.